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Baraitser-Winter cerebrofrontofacial syndrome (BWCFF) (BRWS; MIM #243310, 614583) is a rare developmental disorder affecting multiple organ systems. It is characterised by intellectual disability (mild to severe) and distinctive facial appearance (metopic ridging/trigonocephaly, bilateral ptosis, hypertelorism). The additional presence of cortical malformations (pachygyria/lissencephaly) and ocular colobomata are also suggestive of this syndrome. Other features include moderate short stature, contractures, congenital cardiac disease and genitourinary malformations. BWCFF is caused by missense mutations in the cytoplasmic beta- and gamma-actin genes ACTB and ACTG1. We provide an overview of the clinical characteristics (including some novel findings in four recently diagnosed patients), diagnosis, management, mutation spectrum and genetic counselling.

During 1987 and 1988 First ISLSCP (International Satellite Land Surface Climatology Project) Field Experiment (FIFE) studies conducted in the tallgrass prairie of central Kansas, variations in ungulate grazing intensity produced a patchy spatial and temporal distribution of remaining vegetation. Equally variable plant regrowth patterns contributed further to a broad array of total primary production that resulted in a pronounced mosaic of grazing impacts. This regrowth potential, derived from a relative growth rate (RGR) equation comparing ungrazed and grazed plants, determines much of the ecosystem dynamics within and among the grazed pastures and between years. Rates of change in new plant growth (ΔRGRg) ranged from −100% to +40%; however, 78% of the time in 1987 and 71% in 1988, productivity increased as a function of grazing intensity. Since plant growth potential in ungrazed (RGRug) and grazed systems (RGRg) have inherently different attributes, interactions with the abiotic environment may ...

In tallgrass prairie, high plant species diversity results not from a large number of grass species, but from a large number of forb (nongrass, herbaceous) species. Forbs exhibit morphological, life history, and ecophysiological characteristics that contrast sharply with those of the dominant C4 grasses. Success of the subdominant forbs varies strongly with topographic position and burning regime, and landscape scale patterns of abundance are well documented. But comparatively little is known about the mechanisms determining these patterns in persistent tallgrass prairie forbs. To elucidate these mecha- nisms, (1) leaf-level physiological characteristics of the dominant C4 grass, Andropogon gerardii, and four co-occurring C3 forbs were measured in response to natural and exper- imentally manipulated gradients of N availability, and (2) seasonal light environments of forbs in contrasting topographic positions and burning regimes and their morphological and physiological responses in these environments were compared to determine whether resource availability and utilization patterns contributed to patterns of forb distribution and abundance. The effects of burning regime and topographic position on maximum rate of photosynthesis (A) and stomatal conductance to water vapor (g) measured at the leaf level were not consistent with patterns of forb abundance. Nitrogen did not appear to limit forb physiological processes, even though increased N availability resulted in higher tissue N concentrations and greater biomass. There was no consistent increase in A or decrease in g in response to fertilization. However, A at low light levels was as much as 67% higher in fertilized Vernonia baldwinii and A. gerardii compared to unfertilized plants. Greater light availability to forbs in the canopy was associated with lower grass biomass production in uplands compared to lowlands and in unburned compared to burned sites. Forbs did not appear to adjust morphologically (leaf area and plant height) to different light environments at different sites. As a result, as much as 90% of forb leaf area in the burned lowland was displayed in low light, whereas as little as 30% of forb leaf area was in low light in the uplands at midseason. Estimates of potential whole-plant carbon uptake, based on leaf area distribution relative to available light and A as a function of light availability, agreed well with patterns of forb abundance and production. Differences in light availability may ac- count for much of the variability in forb abundance related to burning regime and topo- graphic position by limiting carbon gain in forbs more in burned lowlands than in other sites.

High plant species diversity in tallgrass prairie results not from a large number of grass species but, rather, from a large number of forb (nongrass, herbaceous) species. Although morphological characteristics of tallgrass prairie forbs differ strongly from those of the grasses and their patterns of abundance vary substantially with burning regime and topographic position, comparatively little is known about the ecology of persistent tallgrass prairie forbs. We measured leaf-level physiological characteristics of the dominant C4 grass, Andropogon gerardii, and five co-occurring C3 forb species in response to burning regime and topographic position to determine if there were either absolute or seasonal differences in resource utilization patterns that could contribute to the patterns of forb distribution and abundance in tallgrass prairie. In a wet year, neither fire nor topographic position affected leaf-level physiological characteristics in the grass and forbs studied, and thus responses were not consi...

We argue that herbivores often induce nonlinear or biphasic growth and development in plants. Collectively these individual responses translate into a system—level optimization curve wherein at low levels of herbivory overall community responses show increases in production potential, whereas extreme herbivory causes extreme reduction in productivity. The transition between these two states defines a point of optimal herbivory in respect to C and N processes.We present four case examples from the literature demonstrating such nonlinear responses, suggesting a widespread existence for this herbivore—plant phenomenon. The nonlinear responses appear to demonstrate temporal and spatial scale dependencies. See full-text article at JSTOR

Remote sensing of grazinglands to obtain estimates of productivity relies entirely upon absorption and reflectance properties of the vegetation and its background to provide accurate qualitative and quantitative values. Interpretations of these signals are highly dependent on vegetation responses to perturbations, such as grazing or alterations in nutrient cycles. If remote sensing models of grassland growth ignore feedbacks derived from grazing animals, or only negative feedbacks are assumed, there is a high likelihood of errors developing during model validation. We review fundamental assumptions made when using remote sensing data from grazing systems and give examples of the problems involved.

Incorrect blood component transfusion is the most frequent serious incident associated with transfusion. Errors responsible for these incidents frequently involve patient misidentification.This study evaluated a barcode patient identification system involving hand-held computers for blood sample collection for compatibility testing and the administration of blood. Audit of practice was carried out before and after its introduction.The baseline audit revealed poor practice, particularly in patient identification. Significant improvements were found in the procedure for the administration of blood following the introduction of barcode patient identification, including an improvement from 11.8 to 100 percent in the correct verbal identification of patients (p/= 0.001). Similar significant improvements were found in matching verbally stated identification details with details on patient identification wristbands, in correct patient identification before the collection of blood samples, and in the proportion of correctly labeled samples. Staff found the barcode identification system easy to operate and preferred it to standard procedures.A barcode patient identification system was found to simplify the clinical transfusion process and improve practice. These results provide support for further work on the development of such systems for transfusion and for other hospital procedures requiring patient identification.

The ability of the growing kitten to digest protein, fat, carbohydrate, dry-matter and energy were assessed. Kittens were divided into two groups; one group was fed a wet diet, the other a dry diet. Both groups were allowed ad libitum access to food. Apparent digestibility of the two diets, and kitten bodyweights were measured over a 24-week period. There were no significant differences in mean bodyweight between the two groups. Digestible energy intake of the kittens decreased with increased age; regression analysis of the data generated two fitted models which appeared to accurately predict the digestible energy intake between 39 and 41 weeks of age. There was a significant (P < 0.05) effect of diet on the apparent digestibility of protein, organic-matter and dry-matter. Age had a significant (P < 0.05) effect on the apparent digestibility of all the parameters measured. Newman-Keuls multiple range tests showed that apparent digestibility of carbohydrate, organic-matter and total energy significantly (P < 0.05) increased in kittens older than 19 weeks. This suggests that the digestive capacity of the younger cat may be affected by the physiological development of the gut, and dietary induced enzyme modulation.

Production of tallgrass prairie vegetation was measured on experimental plots in which defoliation intensity and frequency were manipulated by mowing and using movable exclosures on areas chronically grazed by cattle. Defoliation history largely controlled whether or not defoliated plants overcompensated (exhibited enhanced production compared to undefoliated controls) for tissue removal. Plants on chronically grazed sites only compensated for foliage removed by grazers. Production on plots mowed prior to the year of measurement was similar to that on chronically grazed sites, while previously unmowed plots exhibited substantial aboveground overcompensation. Aboveground production was maximized by the most frequent mowing treatment and by intermediate mowing heights. Nitrogen and phosphorus concentrations and amounts in aboveground tissues were increased by mowing and grazing. Current mowing regime was more important than mowing history in determining nitrogen concentrations except very early in the growing season. Effects of grazing and mowing on belowground biomass were inconsistent, but frequent mowing appeared to limit accumulation of belowground N reserves and biomass. In North American grasslands, overcompensation is a nonequilibrium plant response to grazing. Photosynthate that would be stored as reserves and used for root growth and flower and seed production instead is used to replace lost leaf area, thereby resulting in higher foliage productivity. However, under chronic grazing or mowing, vegetation is prevented from maintaining high nutrient and water uptake capacity (large root biomass) and accumulating reserves that allow overcompensation responses.

β-Galactosidase was found to act on α-lactose slightly more than twice as rapidly as on β-lactose for both the hydrolysis and transgalactosylis reactions. The effect was shown to be on the Vmax values; the Km values for the different anomeric forms were the same. The step of the reaction for which the enzyme has anomeric specificity was shown to be glycosidic bond breakage. The steps in glucose release or in the glucose acceptor reaction were not affected by anomeric composition. Neither allolactose hydrolysis nor transport of lactose into the cells by lac permease was sensitive to the anomeric composition of the substrate. The implications of these results for lac operon induction and for lactose metabolism are discussed.

A graphic summary of the relations of growing ovocytes, mature ova, the fertilization process, the broods of embryos retained in the ovary and the time of birth is offered in Table IV. Each group represents the situation within a single ovary at the height of the reproductive season and at the moment in which a brood is born. The term brood is used to indicate a group of growing and differentiating ovocytes of approximately equal development up to the time of fertilization and also the embryos produced by the fertilization of these ova up to the time for birth. No quantitative relations are implied concerning comparative size of ovocytes or embryos in different species nor of comparative lengths of time that embryos are retained in the ovary.A study of Table IV leaves one with the impression that the extreme type of superfetation in Heterandria formosa might have arisen from the simpler type as illustrated in Pœcilistes pleurospilus. The argument also appears to be defensible that the simpler type of supe...

The first and second abdominal appendages of males are ha bitually modified in Catnbarus for the purpose of copulation. The individual parts of the first pair of appendages are fused and twisted and lie compactly in a groove on the ventral side of the thorax. The appendages of the second abdominal segment re semble the typical swimmeret in general plan (Figs. i and 6). However, the protopodite is elongated and heavier, the basal Un segmented portion of the endopodite is likewise reinforced, bearing a conspicuous triangular shoulder. The terminal segmented por tion of the endopodite is much reduced. The remaining swimmer ets are unusually quite typical. There is apparently only one published record of a modified third abdominal appendage. Moenkhaus, Proceedings of the Indiana Academy of Science, 1903, pp. III and 112, describes a specimen of Cambarusvirilis bearing such a modification as fol lows: “? The first and second pairs of appendages were modified in the usual way and in no way differed from corresponding appendages in the normal male of the same species. The addi tionally modified third pair r@esemble in plan almost exactly the second pair. The exopod and the segmented flabellum of the endopod are much less reduced and much more extensively pro vided with feathered setae than the second pair. They are about the same size and in position converge and fit against the sec ond pair of appendages much in the same manner that these do against the first. Whether they were in any way functional I am, of course, unable to say.― Another specimen with a modi fication similar to but not so fully developed as the one described by Moenkhaus was collected by Dr. H. J. Van Cleave of the University of Illinois and appears in his collection.

anal fins of males and of females are practically identical in structure but the fins of the two sexes become structurally divergent with the ap proach of maturity. Rays 3, 4 and 5 of the male fin undergo elonga tion and six differentiation areas arise within which characteristic hooks, spines, serrae and plates develop. In the female fin there is no marked elongation of the 3—4—5 ray complex and the differentiation areas do not arise to elaborate the morphological features peculiar to them. Regnier (1938) was able to induce the development of some of the gonopodial characteristics of the male in the anal fins of the females of Xiphophorus helleri and Lebistes reticukitus by intramuscular injections of testosterone propionate, thus proving that the genetic factors for a gonopodium are borne by the female but that, in the absence of an androgenic hormone, they are not expressed. Grobstein (1940) ob tained the same result in Platypoecilus maculatus but was able to demon strate in addition that an anal fin of an adult female produced the fea tures of the male gonopodium more exactly if that portion of the fin which gives rise to the male characteristics was cut away and allowed to regenerate during the treatment with testosterone propionate. Ever sole (1939) was able to secure the formation of atypical gonopodia in females of Lebistes reticulatus at various stages by injecting testo sterone propionate peritoneally and by adding testosterone propionate to the ration. The writer is indebted to Eversole for the information that pregneninolone (ethinyl testosterone) and other androgenic hor mones will produce a similar effect. The writer has studied in detail the normal development of the anal fins in males and females of Gambusia affinis affinis (Turner, 1941a) with particular attention directed to the origin of the marked differences

A number of crayfishes belonging to the genus Cambarus in which secondary sexual characters of both sexes were found upon the same individual have been described by Faxon, Hay, Ortman and the writer. All of these specimens with the exception of one described by Hay were females. In some cases there was a full complement of female secondary sexual characters with the addition of one or more male characters and in other cases a female character was lacking while one or more male characters were present. The one exceptional specimen described by Hay was hermaphroditic and possessed both male and female primary and secondary sexual structures. Male crayfishes in the genus Cambarus bearing sexual characters of females have not been noted before and it is the purpose of this paper to describe two specimens which appeared in recent collections made in southeastern Wisconsin. Both specimens were collected from tributaries of the Rock River near Beloit, Wisconsin, the first in July, I923, and the second in July, I924. One is a specimen of Cambarus virilis, 65 mm. long and is a second form male normal in every respect except that an oviducal opening exists upon the left third walking leg. An examination of the internal organs shows a normal spermary and normal spermatic ducts. There is no tube of any kind joined to the oviducal opening at the base of the third walking leg. The second specimen is one of C. propinquus, 46 mm. long, and is identical in its peculiarities with the first specimen described. It is a normal second form male with all the normal internal and external structures of the male but bearing in addition an oviducal opening at the base of the third walking leg. As in the

In the Anablepidae, a family of viviparous Cyprinodont fishes, the mature eggs are fertilized in the ovarian follicles. The embryos are retained in the modified ovarian follicles until birth and are born when about 44 mm. in length. The embryos develop expanded yolk sacs which reach a maximal diameter of about 10. mm. The vitelline veins on the surface of the yolk sac develop rows of bead-like swellings, yolk sac bulbs, which serve to facilitate absorption of materials from the fluid of the follicle cavity. There is an extensive system of follicular villi upon the internal lining of the follicular capsule, the apparent function of which is to increase the vascular surface of the internal lining of the follicular capsule and to facilitate the interchange of materials between the blood of parent and fluid of the follicular cavity. The follicular villi and the yolk sac bulbs develop at the same time. These two adaptations for viviparity are apparently unique in this family of fishes.

The types of viviparity in teleost fishes involve differences in: (1) location within the ovary during gestation; (2) length of period of gestation and maturity of embryos at birth; (3) degree of dependence of embryos upon the maternal parent; (4) degree of modification of the ovarian tissue; (5) periodicity in reproductive cycles; (6) sequence in fertilization, ovulation, hatching, retention of ova or embryos and finally expulsion of embryos. Some of the processes-at least development of ova, ovulation, retention of embryos and expulsion of embryos (birth)-are presumably under hormone control, and diversity in type of viviparity is therefore accompanied by an equivalent diversity in the hormones functioning in the control of reproduction.

Viviparity in the teleost fishes is most highly developed in the family Embiotocidae. In Cymatogaster aggregatus, a member of this family, the males are sexually mature at birth. Females born in June and July are inseminated soon after birth and carry the spermatozoa in the ovarian cavity until December when eggs are fertilized. Embryos are retained in the ovarian cavity till the following spring when they are born. The cells of the epithelium lining the ovarian cavity develop internal fluid reservoirs which reach their maximal stage in early gestation when there is an extensive sloughing of epithelial cells. The epithelium returns to its original condition in late gestation and later the cells undergo multiplication. The stroma becomes swollen and contains a large amount of fluid during early gestation and shrinks as the embryos become larger. Many of the eggs, failing to reach maturity at the time of fertilization, degenerate. Degeneration also takes place in numerous smaller ovocytes during gestation but some of them survive to grow during the next season. The cyclical changes in the ovarian tissue of Cymatogaster aggregatus are parallel to those which occur in the ovaries of the Goodeidae and the Jenynsiidae, two other families in which viviparity has been highly developed.

The Goodeidae are a family of cyprinodonts containing about nine genera and twenty-six species. They are confined exclusively to the Mexican Plateau and to streams in the immediate vicinity. All are viviparous. Fertilization is internal. The eggs are extremely small and contain very little yolk. The embryos are retained in the ovarian follicles until the yolk is practically absorbed, in the meantime developing unique absorptive organs in the form of extensive ribbon-shaped proctodaeal processes. The embryos are evacuated into the intra-ovarian cavity where they are retained for several weeks, during which time the proctodaeal processes become extended. The ovary becomes a nutritive organ and produces secretions which are discharged into the intra-ovarian cavity and absorbed by the embryo through their unique processes. The processes differ in form, number, and histological structure, but are specific in their peculiarities for each species. These specific differences, together with marked differences in the ovary, will furnish a basis for a re-classification of the genera and species of the family. A comparison in made between this family and the other ovo-viviparous and viviparous cyprinodonts, on the basis of which it is concluded that the Goodeidae have arisen separately from an ovo-viviparous ancestor, which in turn was derived from an ovo-viviparous type. A comparison is also made between the peculiarities of reproduction in this family and those of other viviparous teleosts.

During the spring and summer of 1922 and 1923 the writer discovered nineteen specimens of Cambarus propinquus that possessed to some degree secondary sexual characters of both sexes. A close examination revealed that all were functional females, some of them bearing eggs when taken but possessing in addition to the usual female secondary sexual characters from one to three male secondary sexual characters as well. A number of males were found bearing extra male characters and two females with extra female characters. These results led to the exami nation of a fairly large collection of Cambarus virilis which had already been made and also to the search for aberrant conditions whenever specimens came to hand. Next to Cambarus propinquus Cambarus virilis is the most abundant crayfish in southern \Visconsin and the two are usually taken together in the lakes and streams.

In study number three of this series, males of Cambarus propinquusand of Cambarus virilis which bore supernumerary male characters were described. These supernumerary char acters were in the form of copulatory hooks ordinarily found only upon the third walking legs but in these cases present also upon the second or the fourth walking legs. In C. virilis the extra hooks were confined to the second walking legs. In C. propi@@quus the additional hooks were found upon either the second or the fourth walking legs. It was predicted that in C. propinquus, since either the second or the fourth walking legs might function in carrying the extra hooks, specimens might be found in which copulatory hooks would be present upon both the second and the fourth walking legs. During the summer of 1924 large collections were made from practically all the streams and some of the lakes of southeastern

1. The pectoral fins of juvenile males and females in Gambusia are practically identical in structure.2. In Gambusia and in a number of closely related genera a modification of the pectoral fin occurs in the male with the onset of sexual maturity. The structural peculiarities of the character consist of elongation and segmentation of rays 2, 3, 4, and of the anterior branch of ray 5, and the partial separation of the dorsal and the ventral components of these rays, a general widening of the ventral component and a development of an imbricated area by further widening of the ventral components within a localized area.3. Females possess one or more genetic factors for the same structural characters and they can be induced to develop the characters by the application of methyl testosterone or ethynyl testosterone.4. The first stages in the development of the characters are induced in medium sized females by treatment with methyl testosterone at a concentration of 1 mg./20,000,000 cc. of water. A concentratio...

Parabrotula dentiens is a viviparous deep sea Brotulid fish. The embryos at the 6 mm. stage are held within the ovarian cavity as are the embryos of Zoarces, the Embiotocidae, the Goodeidae, the Jenynsiidae and the Anablepidae in the later stages. The embryos of Parabrotula dentiens are equipped with external processes which are attached around the anus and to the ventral wall of the embryo for a short distance in front of the anus. The processes have a spongy connective tissue stroma and are covered with a syncytial layer. It is assumed that the processes augment the body surface of the embryos and have a nutrition-absorbing and an oxygen-absorbing function.

It is necessary to specify the exact meaning of the word when employing the term regulation. Driesch (1901) defined it as a process or a change in a process occurring in a living organism, by means of which a disturbance of its pre-existing normal condition is wholly or in part compensated and the normal condition is reestablished. Roux described regulation as a compensation of disturbance, i.e., the return of the disturbed organism to a type or norm. Roux emphasized the part of heredity in the control of regulatory processes while Driesch was inclined to invoke extrabiological metaphysical controls. Morgan (1898), who had been working in the field of regeneration, coined the term morphallaxis to include the remodelling of old tissue into new forms. He later (1907) extended the use of the term to include re-differentiation and regeneration. Driesch used the terms as a synonym for restitution by redifferentiation. Morgan (1907) assumed that the influence of the formed parts upon the unformed parts during their development was a pressure or some kind of a response to a pressure. Child (1906) after working extensively on regeneration of Planaria and other forms came to the conclusion that living organisms are in a continual state of regulation physiologically and that no particular group of processes could be separated as formative as compared with those which, in the normal adult animal, maintained it in a state of partial equilibrium. Jennings (1905) applied the concept of regulation to the field of animal behavior and concluded that all animal behavior, in its more complex aspects as well as its simpler ones, is attributable to regulation. Experimental embryologists point out (Weiss, 1939) that the course of embryology is rather fixed in animals with a mosaic type of development and that experiments involving interference with the regular course of development are not very productive. Other animals in which the course of development is not firmly fixed at an early stage, referred to as regulative types, will sometimes rearrange the cellular components in excised parts of an embryo and form one or more perfect embryos from material originally destined to form only a part of an embryo. Spontaneous abnormalities in embryos may rearrange their parts so as to form a normal embryo. The term regulation is used to indicate the processes by which the embryos undergoing experimental interference or embryos having spontaneous anomalies rearrange their materials so as to produce perfect whole individuals. It is assumed that the processes and the controls of the processes are identical with those which guide development in the course of normal development. Presumably the regulative mechanism continues to exist in fully formed individuals although, under normal conditions, there is no opportunity for the mechanism to be exhibited. Curtis defines regulation as all of the processes by which the organism returns to the physiological and morphological type that characterizes the species after the

The external secondary sexual characters in the genus Cambarus are so constant in structure and position that they are used extensively for sub-genus and species diagnosis. Some variation has been found in structure, number, and position of these characters, however, in many instances characters of one sex being found on members of the opposite sex. Such variations occur principally in copulatory hooks, oviducal pores, first and second abdominal appendages and, to a lesser extent, in the male genital pores. Variations in the annulus ventralis are extremely rare, records of only four cases being found in the literature. Two additional specimens were recently collected by E. P. Creaser on June 29, 1932. Both specimens were found in one locality, the Huron River, five miles southwest of Dexter, Michigan. These latter two are the only ones seen by the writer in examining more than 75,000 females of the genus Cambarus.

The embryos of twenty-one species of the family Goodeidae have extensive rectal processes (trophotaeniae) which serve as absorptive organs, by means of which the embryos while they are retained in the ovarian cavity absorb substances dissolved in the ovarian fluid. Embryos of three species have not been available for study. No trophotaeniae are present in one species Ataeniobius toweri. There are three general types of trophotaeniae, rosette, sheathed and unsheathed. The structure of the trophotaeniae is sufficiently constant in each species to be used in species determination.

A BATTERY jar containing decaying aquatic vegetation was noticed to contain a large number of midge-like larvae and pupae, and when minute moth-like flies belonging to two different species emerged from the pupa cases the jar was covered to see whether the flies would not breed. The possibility was suggested by the writer having inbred blow flies (Calliphora vomnitoria) for a number of generations in an unsuccessful attempt to secure mutants. Within a few days it was noted that a new generation of larvae had been produced. These were isolated and a careful record kept of the specimens. Sixteen days after the first adults were seen a new generation of adults emerged from the isolated larvae. From these new adults fresh cultures were started, and after two generations of inbreeding a considerable number of white-eyed mutants were observed.' The second species of fly completed its life cycle in a somewhat longer time and produced no mutations. These results demonstrated the feasibility of using the animals for breeding experiments. The two species and the white-eyed mutation have been isolated and maintained as pure strains, the method of inheritance of the white-eyed mutation has been worked out and the reactions of normal and mutant flies recorded. It is intended that the present paper shall be one of a series giving an account of the results obtained.

Differential scanning calorimetry has been used to study the thermal denaturation of ribonuclease in aqueous dimethyl sulfoxide and acqueous p-dioxane. A two-state reversible denaturation occurs in acqueous dimethyl sulfoxide. The denaturation is irreversible in aqueous p-dioxane. The transition temperatuire decreases in both organic solvents, with p-dioxane producing a considerably greater effect. The enthalpy of the denaturation initially increases with increasing dimethyl sulfoxide concentration and then decreases at high concentrations. Similar behavior is observed in the entropy in the dimethyl sulfoxide solutions. The enthalpy of the denaturation decreases markedly with low p-dioxane concentrations. Changes in pH due to presence of organic solvent cannot account for the changes in enthalpy of denaturation. Addition of organic solvent tends to increase the pH of the ribonuclease solution. Higher pH in aqueous solutions gives a high transition temperature, whereas addition of organic solvent results in the opposite bahavior. The relative changes in the two solvents systems suggest that specific solvent effects occur and that destablization of the native state relative to the denatured state is greater with p-dioxane than with dimethyl sulfoxide.