The primary source from which all vaccines are derived is a culture of the organism against infection by which it is desired to protect the animal. The culture may be used as a vaccine either alive or dead.- We are concerned here only with the latter. Such a killed culture comprises the organism itself and the products of its metabolism, together with part or the whole of the culture medium in which it has grown. This mixture may be called a whole vaccine. By appropriate treatment a “whole vaccine,” may be deprived of some or all of such constituents as are not concerned in bringing about, when inoculated into animals, those changes which constitute protection. Such a vaccine may be called a derived vaccine in the case when all the immaterial constituents are not removed, the term antigen being reserved to designate that substance which alone is concerned in conferring protection. The main object of this investigation is the preparation of a derived vaccine with the hope that the antigen may ultimately be isolated.

We have recently had the opportunity of studying a plague epidemic that broke out on Terceira Island, Azores, in 1908. Terceira Island contains a population of 45,000 souls, the epidemic spread over 27 parishes. About 260 persons were attacked, with a mortality of about 48%.

According to Kossel (1888) Fritz Miiller discovered that phthisical sputum digests fibrin and coagulated albumen in weakly alkaline media, but the fact that antiseptic pus digests proteins seems to have been first observed by Leber.

Achalme (1899) separated proteolytic ferments from pus from various sources and Erben (1903) and Schumm (1904) drew attention to the notable quantity of albumoses in blood from cases of myologenous leukaemia which had been incubated, and the relative absence of this proteolysis in the incubated blood from cases of lymphatic leukaemia. Ascoli and Mareschi (1901) showed that the peritoneal exudate produced by aleuronat underwent autolysis under aseptic conditions.

The following statement embodies the chief conclusions which have been provisionally reached by the Advisory Committee as the result of the investigations made under their direction from 1905—1909 into the mode of spread of plague in India.

A stock of 500 guinea-pigs at the Lister Institute was attacked by an epizootic and only 21 survived. These survivors showed definite immunity to a bacillus of the food-poisoning group (indistinguishable from B. aertryck and the B. suipestifer) recovered frequently from animals dying during the epizootic. Five of them have been proved to be carriers excreting the bacillus intermittently five month's later and the serum of all of them agglutinates the bacillus. Spread of infection apparently did not occur amongst contacts placed with these carriers in the few experiments carried out.

Krönig and Paul (1897) were the first to study the process of disinfection by making quantitative observations at intervals during its progress. Their figures showed that disinfection proceeded in an orderly manner and that the rate diminished as the number of survivors became less. Ikéda (1897) attempted to express their results by an empirical formula.

1. An epizootic killing 90% of a stock of 500 guinea-pigs has been described; cultures from these guinea-pigs frequently gave an organism indistinguishable by cultural or serological tests from the B. aertryck and the B. suipestifer.

2. This organism was highly pathogenic when inoculated subcutaneously into guinea-pigs and of low pathogenicity when given to them with food.

3. Healthy contacts put with animals infected subcutaneously or fed with the bacillus did not die.

4. Sterile filtrates of organs of guinea-pigs of the infected stock administered by different methods frequently killed.

5. The evidence definitely suggests that the essential infecting agent in the epizootic was a filter-passer.