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Learning leads to a decrease in program cost and inflation leads to an increase in program cost. At a certain time, the benefits of leaming and the penalty due to inflation will balance each other. This time is defined as the “critical time.” The “critical tune” depends upon the number of ships to be built because this determines the possible gain in learning. The “Critical time” also depends upon the assumed inflation, upon the achievable learning rate, and upon the material/labor ratio of the first ship. Learning expectation can be influenced by planning and the material/labor ration by a make– or buydecision. Assumptions on future learning are as vague as assumptions on inflation. The paper shows that it is almost impossible to beat inflation. It shows that accelerated programs are preferable and that make—decisions supersede the value of buy—decisions. The result is derived from an abstract treatment of the subject.

It has been shown in previous communications (Todd, 1930, a, b ) that the red blood corpuscle of the domestic fowl constitutes a “multiple antigen” of considerable complexity and of so high a degree of specificity that, in unrelated birds, the red cells of any particular fowl can be differentiated from those of any other individual of the same species, by means of a simple agglutination reaction carried out with suitably exhausted polyvalent iso-agglutinating sera. When the birds are closely related, however, this is not always possible, as the corpuscles of certain members of a family may show a very close resemblance. In the course of some earlier experiments, made in order to investigate the hereditary transmission of the characters of the red blood corpuscle, three separate couples of unrelated Plymouth Rock birds were mated, and the cells of parents and offspring in each of the three families examined in detail (Todd, 1930, b ). On reviewing the results obtained and com­paring the behaviour of the corpuscles of the individual members in anyone family, it was seen that the cells of no two chicks appeared to be exactly alike, but that there was always some degree of difference, varying from a close resemblance to a very marked contrast; suggesting that the red cells contain a number of different antigenic units, each of which behaves independently during the process of hereditary transmission.

In a previous communication (Perdrau and Todd, 1933), dealing with the photodynamic action of methylene blue on bacteriophage, we have recorded the results of experiments confirming the observations of Clifton (1931), both as regards the part played by visible light in bringing about the reaction and also as regards the necessity for the presence of free oxygen. In the course of these experiments it was found that while the free phage is highly sensitive to the photodynamic action of methylene blue, it becomes very much more resistant to the dye in the presence of the corresponding living bacterium. This protection of the phage is only exercised by living bacteria, killed organisms being without effect. It is, moreover, not a strictly specific phenomenon, as protection is in some cases brought about by bacteria other than those for which the phage has been prepared. In view of the many similarities of behaviour shown by the bacteriophage and the ultramicroscopic viruses, it seemed not improbable that some of the latter might be susceptible to the photodynamic action of methylene blue, and tests were accordingly made with such viruses as we had at our disposal.

The term “Isolysin” was first employed by Ehrlich and Morgenroth in the third of their now classical series of papers entitled “Studies on Haemolysis(1).” It had been shown by Bordet that if the red blood corpuscles of an animal A are injected into another animal B, of a different species, the serum of B develops a haemolysin for the corpuscles of A. This haemolysin being produced in a different species of animal from that yielding the corpuscles, is termed, according to Ehrlich's nomenclature, a heterolysin.

The following is a brief account of some results obtained during the course of an investigation in to the artificially produced hæmolytic isolysins of the ox. The peculiar interest attaching to this class of bodies was first pointed out by Ehrlich and Morgenroth in their classical studies on hæmolytic, where they showed by the treatment of goats with large quantities of laked goats’ blood, that hæmolytic isolysins were formed in the blood of the immunised animals. Their investigations were made with sera prepared in this way.

It is now generally assumed by the majority of workers in the field of virus diseases that the term “ virus ” should be limited to those small organisms, either approaching or below the limit of ordinary microscopic visibility, which are incapable of multiplication in vitro except in the presence of living animal or vegetable cells. This limitation is obviously only provisional, as with a fuller knowledge of the conditions obtaining in the living cell it may at some time become possible to simulate these sufficiently closely to allow of the growth of the virus in a cell-free medium. Until this is accomplished, however, the presence of the living cell must be regarded as essential, and we are faced with the problem of elucidating its role in the multiplication of the virus.

Many deaths occur every year in Egypt as the result of scorpion sting. These deaths are practically confined to Cairo and Upper Egypt, and are almost entirely among children. Unfortunately, owing to local conditions, it is almost impossible to obtain really accurate figures for this mortality, but some idea may be formed from the statistics given below of some of the larger towns.

In a paper published last year the authors described a method by which it is possible to recognise the red blood corpuscles of any individual ox and to differentiate them from those of any other member of the same species. The method depends upon the fact that if a highly polyvalent isohæmolytic serum is treated repeatedly with the red blood corpuscles of any individual of the species for which the serum has been made, it entirely loses its hæmolytic action for the corpuscles of all other individuals of the same species. Such a serum therefore constitutes, so to speak, a specific reagent for the corpuscles of the individual for which it has been prepared, and by its means one is enabled to follow up and to identify these corpuscles even in the presence of corpuscles of other individuals.

In the course of some work on the trypsin susceptibility of two races of staphylococcus bacteriophage, Schultz and Krueger (1928) made the observation that these two phages were remarkably sensitive to the action of methylene blue─being completely inactivated within 6 to 12 hours by concentrations of the dye as low as 0.002 per cent. So far as their tests went, the susceptibility to methylene blue appeared to be peculiar to the two races of staphylococcus bacteriophage, as eight phages for other organisms were entirely unaffected by the dye. Moreover, of a considerable number of dyes used, methylene blue was the only one showing this action. Clifton and Lawler (1930) and Burnet and McKie (1930) repeated these experiments with methylene blue and other dyes on several strains of bacteriophage, but they were then unaware of the role played by light in these reactions. A new aspect of the mechanism of the reaction was opened up by Clifton (1931), who found that no inactivation took place when the dye and the phage were mixed, incubated and tested in the dark ; but that an exposure of 5 minutes, or even less, to indirect sunlight before incubation resulted in complete inactivation of the bacteriophage. He also showed that the presence of oxygen was necessary for the process, as inactivation did not occur in vacuo or in an atmosphere of nitrogen, and was inhibited by reducing agents such as cysteine hydrochloride. He therefore concluded that the inactivation of the staphylococcus phage by methylene blue is due to an oxidation of the phage by photosensitized methylene blue in the presence of oxygen.

In this outbreak of diphtheria certain individuals suffered from diphtheria, and others from sore throat probably diphtheritic. These individuals obtained their milk supply from two cows. Members of one household who did not drink milk, or who used it only after sterilisation, escaped infection. The cows yielding the milk were found to be suffering from an eruptive disease of the udder, and both from the lesions and from the milk cultures of virulent diphtheria bacilli were isolated. The pathological condition in the cows preceded, by a short interval, the onset of the disease in the patients. Having regard to Power's epidemiological investigations, and to Klein's experimental work, this observation was of the greatest interest and naturally suggested the hypothesis that the lesions were due, primarily, to a specific diphtheritic infection of the cow. Further investigations weakened this view, for it must be noted:—(1) That in a cow intentionally submitted to infection from the diseased cows and in which there occurred the eruptive condition of the udder, neither in the vesicular nor in the ulcerative stage of the disease could diphtheria bacilli be demonstrated.(2) That in calves infected with the eruptive disease no diphtheria bacilli could be demonstrated.(3) That in a calf, in spite of the fact that it had received 10, 000 units of diphtheria antitoxin, the vesicular eruption was experimentally produced. The last is probably the strongest point in support of the dual nature of the condition in the cows.It is conceivable that pathological lesions in the cow such as those described, if infected with the diphtheria bacillus, might form a suitable nidus for its growth and permit of the infection of large quantities of milk over a considerable period. Though we have as yet no evidence on the subject it is possible that a profound change in the virulence of the diphtheria bacillus for the human subject might be effected by such passage through the cow1.The disgusting habit the milkers in this part of England have, of spitting on their hands before milking, would easily account for the infection of the lesions, even in the absence of obvious diphtheria in the cowman; knowing, as we now do, that apparently healthy individuals are not uncommonly the hosts of the diphtheria bacillus.The experiments made with the view of ascertaining whether the eruptive condition was genuine cowpox, are opposed to that view; for two calves, and one cow successfully infected with the eruptive condition and subsequently vaccinated with vaccine lymph, developed a typical vaccinia.The somewhat limited time and material available have prevented us from investigating the matter so fully as we should have wished, or on a scale proportionate to its interest and practical importance. We hope at some future time to go further into the matter.Our best thanks are due to Mr Sidney Villar, F.R.C.V.S., for bringing the outbreak to our notice, and for his help in the veterinary side of the question; and to Dr Carson Smyth for his kindness in allowing us facilities for taking cultures from the throats of his patients.

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One of the most striking points in the pathology of Bacterial Dysentery is the fact that while the bacilli are found regularly in the mesenteric glands, they are not found in the spleen or other organs, and do not occur in the blood, urine, or milk. In this respect Lentz (p. 320) points out that the disease differs markedly from the septicaemic diseases, such as typhoid, and that it must be regarded as a local infection of the intestinal mucous membrane and corresponding lymphatic glands by the bacillus, the toxin alone passing into the circulation and giving rise to the typical clinical picture, which, as in the case of cholera, gives the impression of a severe poisoning or toxaemia.

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The outbreak of cattle plague in Egypt and the establishment of the Serum Institute at Abbassieh offered a suitable opportunity for investigating some points concerning the nature of the causal agent of the disease, and especially the important question whether the virus is, or is not, capable of traversing a filter candle. On this point the literature is strangely contradictory.

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EPIDEMICS of “Furunculosis of the Salmonicidae” generally attributed to a well-defined bacterium— B. salmonicida (Emmerich and Weibel, 1894)—have been the cause of a high mortality among salmon and trout in England during recent years and have been difficult to deal with owing to a lack of know ledge of the epidemiology of the disease and particularly of the reservoirs of the infection during inter-epidemic seasons. The problem of following out the infection is not easy as B. salmonicida has no saprophytic existence in river water, in which it does not live for more than a few days, so that it is useless to attempt the isolation of the bacillus from the suspected water—even if this were a practical possibility. Moreover, the absence of sick or dead fish does not exclude the possibility of infection, as apparently healthy fish are known to act as carriers of the disease and to be capable of spreading the infection.