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Once it has been demonstrated that under appropriate conditions superinoculation of a rabbit with an advanced syphilitic infection may give rise to a typical primary lesion,1the question naturally arises as to whether this second infection is limited in its effects to the local reaction or is capable of further participation in the disease produced.The problem was approached by a number of experiments. Rabbits infected with strains of low virulence were reinoculated with strains of high virulence after the original infection had become well established. In general, the primary inoculation was made in one or both testicles while the second was intracutaneous on the sheath or at the base of one ear, using equivalent amounts of a testicular emulsion. The infections thus produced were compared with those in a series of control animals. The interpretation of the experimental results was based upon the usual course of the disease produced by each strain with particular reference to the type and severity of lesions and to their time and sequence of occurrence since at a given time and under given conditions these are comparatively constant properties of any given strain.The experiments up to the present time have yielded a number of instances in which the nature of the infection differs from that ordinarily seen with any one of the several strains employed and this may be illustrated by citing a single example. The two strains used in this experiment have been studied in a large series of animals. The less virulent strain (111) used for the primary inoculation was isolated in the fall of 1919. It has always produced a mild infection with slight primary lesions of short duration and generalized lesions of a minor character consisting of occasional small diffuse or papular lesions of the skin, slight infiltrations about the sheath, a few cases of keratitis and two instances of slight periostitis of the nasal bones.

The study of tryparsamide as an agent for the treatment of trypanosomiasis and syphilis is now approaching a decisive stage, having passed successively through a period of laboratory investigation and a period of preliminary clinical investigation. The results that have been reported on the one hand by Pearce,1 by Chesterman2 and by Smillie,3 and on the other by Lorenz, Loevenhart, Bleckwenn and Hodges,4 and by Moore, Robinson and Keidel,5 supplemented by numerous personal reports from still other clinicians, leave little doubt that, used with discrimination, tryparsamide will prove valuable in the treatment of human and animal trypanosomiasis and of certain forms of syphilis.Thus far, each step in the progress of these investigations, from the synthesis of the drug to its application to the treatment of diseases, has proceeded as a logical development, based at first on pure experimental evidence and later on clinical experience

Although the iodids have been employed in the treatment of syphilis for many years, their mode of action is still obscure. Clinical experience has shown that iodin compounds have little or no therapeutic effect in the early stages of the disease, due, it is asserted, to the absence of spirocheticidal action; and experimental confirmation of this opinion has been brought forward by Nichols,1 who found that the administration of the amount of potassium iodid tolerated by the body (rabbit) was without effect on the number and motility of the spirochetes of the primary chancre. On the other hand, Neisser2 reported that it was possible to prevent syphilis in the monkey with potassium iodid, if massive doses of from 7 to 8 gm. were administered subcutaneously at the time of or four days after inoculation; that is, no primary lesion was obtained; but Neisser does not state whether secondary

Syphilis in the human subject is characterized by the occurrence of a succession of lesions of various types which follow one another in a more or less orderly progression from the chancre to the terminal stages of the infection, and while to each period of the infection certain types of lesions have been assigned, the order of their appearance is not entirely fixed nor can one say just what lesions may be expected to occur in a given case.The factors that determine these features of the disease may be numerous, and the results of their action differ so widely that diversity rather than uniformity has come to be recognized as one of the most fundamental characteristics of syphilis. The causes which underly this diversity of clinical types are but little understood. It is of course obvious that there are two sets of factors which may contribute to this condition,

The idea of an inhibitory influence has been suggested as a means of explaining certain phenomena of syphilitic infections and there is some experimental evidence on which to base such a conception. The difficulty has been that most of the evidence cited in support of this theory was susceptible of more than one interpretation. This applies in particular to reinoculation and superinfection experiments which have been the favorite means of demonstrating inhibitory effects. Nowhere, however, is the action of such an influence more strongly suggested than in the experimental infection produced in the rabbit by scrotal or testicular inoculations of well adapted strains of Spirochaeta pallida.As it is ordinarily seen, the two most striking features of this infection are an extremely marked reaction at the site of inoculation and a total absence of generalized manifestations of disease. If one considers these peculiarities of the experimental infection as compared with

Since it was first shown that rabbits were susceptible to infection with Spirochaeta pallida, numerous attempts have been made to devise means of producing an infection of the central nervous system in these animals which might be utilized in studying this phase of human syphilis. For the most part, the experiments which have been carried out appear to have been based on the assumption that this could not be accomplished by a simple testicular or scrotal inoculation, but that it was necessary to resort to some intensive form of inoculation, such as an intravenous, intracardial or intracranial inoculation or to the use of repeated inoculations of various kinds. This idea may be accounted for in part by the use of recently isolated strains of Spirochaeta pallida and in part by the apparent inability to produce a generalized disease in the rabbits by ordinary methods of inoculation.How successful these efforts

The present study of the action of tryparsamide in human trypanosomiasis concludes a series of chemical and biological investigations in a particular problem of chemotherapy and thus represents the final step in a logical method of approach to such a problem. It has been shown that tryparsamide, the sodium salt of N-phenylglycineamide-p-arsonic acid, possesses a marked trypanocidal activity in human trypanosomiasis caused by Tr. gambiense. Single doses of from 0.5 to 5.0 gm. produced a peripheral sterilization of lymph glands and blood in an average of 6 to 12 hours. The duration of the peripheral sterilization following single doses of 17 to 83 mg. per kilo ranged from 17 to 58 days in patients who ultimately showed a return of trypanosomes to the peripheral blood. In a number of patients, however, treated with single doses of 9 to 68 mg. per kilo, no such relapse was detected during an observation period of from 40 to 111 days. The drug is extremely soluble in water and may be administered intramuscularly as well as intravenously. The immediate trypanocidal action after intramuscular administration was as rapid as that following the intravenous route while the duration of peripheral sterilization was appreciably longer. Relatively few repeated doses produced in advanced cases a marked and rapid diminution of the cells of the spinal fluid and were associated with definite improvement of mental and nervous symptoms. The occurrence of visual disturbances in certain advanced cases was the only untoward effect detected during the course of the work, and was apparently related to a too frequent administration of the drug. The condition was transitory in the majority of instances and resumption of treatment was not followed by a recurrence of this symptom. The general beneficial effect of the drug was a noticeable feature of its action in both early and advanced cases as shown by the disappearance of subjective symptoms, by the return of the pulse and temperature to normal limits, by the pronounced improvement of the blood picture, and by well marked gains in weight.

The results of serum neutralizing tests with the viruses of pox, vaccinia, and virus III disease herewith reported generally agree and supplement the results of reinoculation experiments on immune rabbits reported in the previous paper (1). The finding that pox virus is neutralized by pox immune serum indicates that the refractory state of recovered pox rabbits to reinoculation with pox virus and the failure of recovered pox rabbits to contract a second pox infection after adequate exposure is to be explained upon the basis of the development of an active immunity. The failure of virus III immune serum to neutralize pox virus is in agreement with the previous conclusion drawn from the positive results of reinoculation and exposure experiments that there is no specific relationship between pox virus and virus III. Rabbits which had recovered from a pox infection were completely refractory to inoculation with dermo-(culture) vaccine, while rabbits which had recovered from vaccinia were partially refractory to inoculation with pox virus. Vaccine immune adult rabbits did not show any clinical evidence of pox upon exposure to florid cases, but young recently weaned vaccine immunes developed definite although comparatively mild pox infections. The serum neutralization tests showed that pox immune serum neutralized vaccine virus although the action was not complete as shown by the positive results obtained with high dilutions of serum; vaccine immune serum possessed some but comparatively slight neutralizing properties against pox virus. The results of the crossed inoculation and serum neutralizing experiments with pox and neurovaccine viruses resembled those obtained with pox and dermo-(culture) vaccine but the differences were less pronounced. The differences in virus neutralizing ability on the part of the three immune sera paralleled the differences in virus potency as indicated by the character of the local lesions at the site of injection and by the general character of the clinical manifestations of the infection. The potency or virulence of pox virus was much greater than that of neurovaccine and vastly greater than that of dermo-(culture) vaccine. The complete identity of pox and vaccine virus could not be established, but a definite relationship between them was demonstrated and this was shown to have an immunological basis. From a practical standpoint vaccination with vaccine virus as a prophylactic measure against rabbit pox was clearly indicated.

The white mouse, the guinea pig, the calf, and probably the rat, were found to be susceptible to infection with the virus of rabbit pox. Serial transmission of the virus in mice by brain to brain passage was characterized by a fatal outcome usually on the 5th or 6th day after inoculation. Infection of the guinea pig was accomplished by intratesticular injection and the virus was continued to the 2nd passage in this species. Guinea pigs developed a well marked cutaneous reaction from the intradermal injection of both rabbit and guinea pig tissue virus. Active virus was demonstrated in the testicles of rats 8 days after intratesticular injection by rabbit subinoculation. In the calf inoculation of the scarified skin was followed by the development of large papular lesions with marked hemorrhage and necrosis. The results of the investigations on the etiology of rabbit pox and of the experimentally induced infection reported in this and the four preceding papers (1–4) are discussed with special reference to the relation of pox virus to other viruses and of rabbit pox to other pock diseases.

Experiments are reported in which it was shown that rabbits which had recovered from experimental or spontaneous rabbit pox were refractory to inoculation of pox virus injected by various routes, and in addition did not develop clinical manifestations of the disease under conditions of exposure to florid cases of pox. It was found that pox recovered rabbits were susceptible to inoculation with the virus of virus III disease of rabbits and that virus III recovered rabbits could be successfully inoculated with pox virus. Furthermore, virus III recovered rabbits developed pox when subjected to room exposure in the same manner as did normal rabbits. It thus appears that there is no specific relationship between the two viruses. Rabbits which had recovered from experimental or spontaneous pox were found to be just as susceptible to inoculation with the virus of infectious myxoma of rabbits as were normal rabbits, a result which demonstrates that there is no specific relationship between these viruses. Rabbits which had recovered from experimental or spontaneous pox were refractory to inoculation with culture dermovaccine virus, but vaccine recovered rabbits were not completely refractory to inoculation with pox virus. Under conditions of exposure to clinical cases of pox, adult vaccine immune rabbits did not develop clinical manifestations of pox, but young, recently weaned vaccinated rabbits did contract mild but definite clinical pox. Experimental pox recovered rabbits were partially refractory to inoculation with neurovaccine virus and neurovaccine recovered rabbits were partially refractory to inoculation with pox virus. The refractory condition of the pox immune rabbits appeared to be more pronounced than that of the neurovaccine immunes. The cutaneous lesions which developed from the intradermal injection of pox, neurovaccine, and culture vaccine viruses showed definite differences with respect to the rate and persistence of active growth, amount of edema, hemorrhage, and necrosis, and the degree of tissue destructiveness. These features were most pronounced in the lesions of pox virus and were least marked in the lesions of culture vaccine virus. The differences were particularly apparent in normal rabbits, but they were also present in the lesions which developed in immune animals. It was found that the calf was susceptible to inoculation with pox virus applied to a scarified skin area. There were many similarities in the appearance and course of the pox lesions to those resulting from culture vaccine virus, the New York Board of Health vaccine, and neurovaccine virus similarly inoculated. But the pox lesions were most numerous, much the largest and most destructive, and by far the most persistent while next in order were those of the Board of Health dermovaccine. The results of these various experiments showed that a close relationship obtains between pox virus, on the one hand, and vaccine virus and neurovaccine virus, on the other, but it cannot be said that pox virus is identical in all respects with either one of these viruses. The findings indicated that the relationship between pox and neurovaccine viruses is closer than that between pox and culture vaccine viruses. Upon the basis of the results observed in culture (dermo) vaccine immune rabbits inoculated with or exposed to pox, it appeared that vaccination with vaccine virus offered a method of protection against rabbit pox.

Experiments are reported in which was studied the effect of a concomitant infection, vaccinia, upon the syphilitic reaction of rabbits. Vaccine virus was inoculated intracutaneously on the side of the body at the time of intratesticular inoculation with Treponema pallidum. The results showed clearly that the vaccination caused a profound disturbance in the syphilitic reaction, the ensuing syphilis being extremely severe. From an analysis of various features of the reaction, it appeared that the factor of host resistance was primarily concerned in the effects observed.

Experiments are reported in which were studied the course and character of a transplantable malignant neoplasm in normal rabbits and in rabbits immunized with a filterable virus, Virus III. The disease which developed in immunized rabbits was extremely mild and much less severe than in normal animals. The effect upon the tumor process displayed by Virus III immune rabbits in the direction of diminished malignancy is considered to be entirely non-specific in character, and the suggestion is made that it is accomplished through a more effective resistance of the host.

A study of a malignant disease in rabbits has been made with reference to the presence or absence of a filterable virus, Virus III, in the tumor. The results are analyzed from the standpoint of certain characteristic features of the tumor process in order to determine any differences in degrees of malignancy. It was found that a more severe disease developed in the series in which the virus-bearing tumor was used than in the series in which the tumor was free of the virus, although the differences were not very marked and were not entirely constant. The influence of Virus III as a factor affecting malignancy has been discussed from the standpoint of its possible effect upon (α) the tumor cells and (b) the host reaction. It has been suggested that the greater malignancy of the pathological process usually induced by the virus-bearing tumor is attributable to a change in the response of the host to the tumor, which change is of the nature of a decreased resistance associated with the reaction of the host to the virus infection.

It has not been possible to propagate a malignant neoplasm of the rabbit with cell-free filtrates, or desiccated tumor tissue or by the use of fluid media kept in contact with tumor tissue. These findings confirm the results of previous experiments carried out with early generations of the tumor. The existence of an agent distinct from the tumor cell which could initiate growth has not been demonstrated. The experiments bring out an essential biological difference between this mammalian neoplasm which is considered to be of epithelial origin and certain filtrable tumors of fowls which have been classified as sarcomata.

A series of experiments was carried out for the purpose of determining whether the reaction of rabbits inoculated with Treponema pallidum might be influenced by their light environment. The conditions compared were (1) diffuse sunlight filtered through window glass and subject to variations due to natural causes, (2) constant and continuous exposure to artificial light with a wave-length of from 3022 to 5790 Ångström units (Cooper Hewitt), and (3) complete exclusion of light. The results showed clearly that each of these conditions produced a distinctive effect and that the effect tended to conform to the nature of the environmental condition. In general, the efficiency of the reaction to infection increased with the amount of light received and with the constancy of the exposure.

An experiment is reported in which an environment of constant and continuous light excluding the shorter ultra-violet rays, and one of constant darkness, have influenced the course and character of a malignant disease of rabbits induced by a transplantable neoplasm. Under the influence of constant light the level of malignancy was observed to be low; under the influence of constant darkness the level of malignancy was somewhat lower than in the control animals living under ordinary indoor light conditions, but the level was not as low as among the animals constantly illuminated. These observations furnish experimental evidence in support of the idea that there is a correlation between the external factor of light on the one hand and the manifestations of an experimental malignant disease on the other.

Data from 645 normal rabbits were used as the basis of an investigation of the relation existing between body and organ weights. Actual and relative weights were correlated with both gross and net body weight. The results obtained varied with different classes of organs but it was found that, in general, there was an agreement between the form and degree of the correlation shown and the structural and functional properties of the organs concerned.

Records of organ weights of normal rabbits covering a period of 3½ years were analyzed with a view to determining first, whether any significant variations of an orderly character could be demonstrated and, second, the general trend of the variations that occurred. It was found that many organs showed decided variations in weight which assumed the form of definite annual cycles. In addition, there was some evidence of a second cycle covering a period of years. These changes were most marked in the case of the endocrine glands (including the testicles), the lymphoid organs, and the liver.

A study of organ weights was made on a group of 295 normal rabbits for the purpose of determining whether any relation could be detected between the weights of organs and the extent and activity of the lesions found post mortem. The results obtained seemed to indicate that disease, even in its mildest form, is capable of affecting the weights of organs that are not directly involved by the disease process and that the effect produced bears a relation to both the extent and the activity of the lesions present. There was also some evidence that the converse might be true; namely, that the occurrence and subsequent course of disease may be influenced in some measure by the state of organ balance and the ability of the animal organism to adjust itself to meet the demands of disease-producing agencies.

A melanotic tumor developed in a defective eye of a syphilitic rabbit following repeated genital inoculations with Treponema pallidum. The appearance of the tumor coincided with the development of a syphilitic lesion in the same eye, suggesting a relation between the occurrence of the two lesions.

The results of a second series of organ weight determinations on normal rabbits are reported and the values obtained are compared with those for the first series. Figures are also given which represent the results obtained by combining the two series of animals or from weight determinations made on 645 apparently normal rabbits selected from stocks used for various experimental purposes.

Experiments are described in which the thyroid or thymus gland of rabbits was removed prior to inoculation of the animals with Tr. pallidum. The effect of these procedures is described from the standpoint of the manifestations of the disease. After complete thyroidectomy, the disease was considerably more severe than in the controls and very markedly so in certain instances. Partial tyroidectomy, on the other hand, resulted in a milder disease than that of the controls. The effect of complete thymectomy was less pronounced than that of either complete or partial thyroidectomy, but, in general, the syphilis resembled that in partially thyroidectomized animals. These effects are discussed in relation to the host's reaction and resistance to experimental syphilis and the conclusion was reached that the integrity and balance of the glands of internal secretion play an important rôle in the mechanism of defense against this infection.

We have found in the kidneys of twelve supposedly normal guinea pigs, coming from Pennsylvania and New Jersey, a parasite that closely resembles in some of its phases Klossiella muris, described by Smith and Johnson, and the renal parasite of two West African guinea pigs, described by Seidelin. The forms most commonly found by us and described as the sporoblast cycle, are evidently similar to those described by Smith and Johnson and by Seidelin. There are certain discrepancies of measurement between the parasite described by Seidelin and the one here described, but the most important difference between the two is the different number of sporozoites resulting from a final division of the daughter sporoblasts. Seidelin has found thirty sporozoites; we have found from eight to twelve, while the usual number is eight. Further, we have found a ring form which is unlike any of the stages in either the sporoblast or schizogonic cycle, and which we interpret tentatively as the male element or microgamete. In addition, we have found a tubular form which resembles the glomerular body of Klossiella muris and which we think is the schizogonic phase of this parasite.