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Extracts of desiccated embryo skin and placenta have been found to exert a definite retarding action on the growth of two transplantable carcinomas of mice, but they were without effect on sarcomas. In tests involving some 828 inoculations of the tumor cells and the extracts, complete suppression of growth occurred in from 55 to 71 per cent of instances, as compared with 21 to 27 per cent in the controls, and where growth was not completely suppressed some retardation was found in practically every instance. To judge from findings in rabbits the inhibitor is not demonstrable in the placenta until the beginning of the second third of pregnancy, reaches its maximum by the last third, but disappears about 2 or 3 days before term. Extracts of fresh placenta are without effect, and no very definite inhibition was noted in extracts of a variety of other desiccated or fresh tissues. The conclusions here reported are based on the results of over 3800 inoculations.

Extracts of desiccated homologous embryo skin and placenta decrease markedly the rate of postoperative local recurrence after the surgical removal of spontaneous cancer of mice. Autografts after a short period of contact with these extracts either failed to grow, or, in the majority of instances, their subsequent growth was definitely retarded. Intraperitoneal injection of the extracts was followed by cessation of growth of established tumors in more than two-thirds of the animals treated, and among these many of the tumors regressed and over 20 per cent were completely absorbed. Tumor mice treated with either extract rarely developed new malignant foci, though this happened frequently in untreated mice.

Following single intravenous injections of a foreign protein antigen, bovine γ-globulin, into mice and rabbits, antigenic material persisting in the liver could be detected for several weeks. Ground liver tissue—taken from the mice and rabbits, just mentioned, either 4 or 6 weeks after injecting the antigen—when transferred repeatedly, at 2 or 3 day intervals, to the peritoneal cavities of normal, or unilaterally adrenalectomized, recipient mice, rendered the recipients sensitive to active anaphylaxis when they were challenged after a suitable interval by intravenous injections of the original antigen. The work throws some light on the state of the antigenic material that persists for 4 to 6 weeks in the livers of the donor animals. Obviously it is sufficiently unchanged, at least in its reactive groups, to engender in the recipient mice antibodies capable of reacting with the original antigen.

A sensitive biological test has been used to detect the persistence of minute traces of a foreign protein, bovine γ-globulin, in the blood and livers of rabbits intravenously injected with it, as an antigen. At various intervals after injecting these rabbits (donors) serum or liver tissue was transferred from them to the peritoneal cavities of normal or unilaterally adrenalectomized mice (recipients) with the aim of rendering the latter hypersensitive to the antigen that might be persisting in the transferred materials; a state of affairs detectable, 2 days later, by the appearance of signs of reversed passive anaphylaxis when the recipient mice were intravenously challenged with a strong anti-bovine γ-globulin rabbit serum. The protein persisted in the blood of the donor rabbits, in readily demonstrable amounts for 1 month, and in the blood of one animal, in minute traces, or as long as 6 weeks. It was detectable in the livers for 8 weeks. The persistence of bovine γ-globulin in rabbits, which form circulating antibodies to it well, is not as long as that in mice, which form antibodies to it poorly, since in previous work with the mouse the antigen was found (1) in the blood after 8 weeks and in the liver for 14 weeks. Nevertheless the antigen persists in the rabbit much longer than is generally supposed. Indeed it can be found in the liver all through the period in which circulating antibody is demonstrable in the blood. Explanations for the phenomenon have been suggested. Its significance in relation to the mechanisms of antibody formation is obvious.

Numerous attempts have been made by us to separate from the cells of a tar sarcoma of the chicken (Chicken Tumor 9) a causative agent for the growth. Experiments with filtrates and desiccates injected as such or in combinations with embryonic tissues have all failed to give positive results. So too have injections of filtrates and desiccates into developing chick embryos failed to yield a response. The results confirm those of previous work with the tumor in this laboratory. The growth would appear to differ in a fundamental respect from all tumors of the fowl previously studied.

A localization out of the blood stream of the agent causing a chicken tumor, with the subsequent development of the growth can be brought about in the breast muscle, by inducing in this tissue a reaction by such substances as Scharlach R, tar, embryonic tissue and kieselguhr. Localization in the reaction tissue elicited by kieselguhr takes place relatively infrequently. The earlier stages of the reaction induced by these substances localize the tumor agent more regularly than the later stages of the reaction.

Animals subjected to dry heat for a short period show a sharp fall in the total white blood count, both the polymorphonuclear leucocytes and the lymphocytes taking part in the fall. Following this there is a slow recovery on the part of the polymorphonuclear leucocytes, which generally require several weeks to regain their normal number. The lymphocytes rise rapidly after the initial fall and continue to rise for 2 or 3 weeks. This increase often amounts to a gain of over 200 to 300 per cent above the normal count for the animal. The observations were made on mice, rats, and guinea pigs. The circulating lymphocytes during the more active stage of stimulation after heating show numerous examples of amitotic division.

Spontaneous cancers were removed from a series of mice by operation. The animals were then subjected to an exposure to dry heat at a temperature ranging from 55–63°C. for 5 minutes. Immediately afterwards a graft of the original tumor was returned. The mice so treated exhibited a marked increase in their resistance to the growth of the cancer graft, over 59 per cent remaining entirely free from a return of the cancer. In a control series in which no treatment was given 96 per cent of the animals showed a return of the cancer.

Mice with high lymphocyte counts and increased activity of the lymphoid tissue induced by one exposure to intense dry heat exhibit a marked increase in the resistance to large doses of bovine tubercle bacilli as compared with that shown by control animals given a similar inoculation. This resistance, judged by the time of survival after inoculation, is increased from two- to threefold. The average length of life after inoculation for three groups of heated mice was 88, 69, and 67 days respectively, while the control groups averaged 16, 29, and 28 days respectively.

The marked and durable stimulation of the lymphoid elements induced by dry heat applied to the animal results in the establishment of a high degree of immunity to certain transplantable cancers in mice. This immunity is evident when the tumor used gives a low, as well as when it gives a high percentage of takes.

Extracts prepared from the testicle tissue of the rat, rabbit, fowl or bull, injected together with extracts of Chicken Tumor I or with cells of this tumor, showed no definite effect of either enhancement or inhibition as concerned the resulting tumors.

The inhibiting factor present in certain relatively slow-growing strains of Chicken Tumor I and in Chicken Tumor X is adsorbed from extracts of the desiccated tumors by aluminum hydroxide (Willstätter Type C) and can be released in effective quantities from this combination by treatment with basic sodium phosphate.