ically and physically the same as some of their best nutrients—save in having opposite powers of rotation.
Taking into consideration that micro-organisms can withstand temperatures and chemicals fatal to man, the slow development of infectious diseases is most probably intimately connected with an insufficiency of assimilable food. This food it may be assumed can only be obtained by symbiosis either with other micro-organisms or products of cell activity in the system itself.
It is claimed that the Anopheles mosquito is the intermediate host of the human malaria and the Culex that of the bird, but not vice versa. These mosquitoes undoubtedly do not select the spores of their respective parasites and avoid the others, but there must exist conditions in the system of the respective mosquito which allow of the propagation of one kind and not the other—and these conditions, I take it, are food assimilable ones.
White mice are immune to splenic fever, other mice very susceptible. Since the blood of white mice is more alkaline than that of the others—and such blood when made less alkaline becomes a good medium for the cultivation of the anthrax bacillus—it has been claimed that the alkalinity produces the immunity. On the other hand it has been found that alkalies are not particularly harmful to the anthrax bacillus—therefore, it seems to me, that alkalinity, as such, is less of a factor than its consequent effects upon the nutrients of the bacillus.
Pasteur demonstrated that micro-organisms select one of two optical isomers, and Fischer proved that it is not only a question of optical antipodes in different sugars, but amongst a great number of geometrical forms few fulfil the requirements of the cells—furthermore he is of the opinion that many chemical processes in the system are affected by molecular geometry.
The albuminoids are the most important constituents of the living cells and since they are synthetically formed from the carbohydrates of the plants, Fischer believes that the geometrical structures of their molecules, as far as asymmetry is concerned, are essentially like those of the natural hexoses. Thus it seems that configuration plays a most important role in making food assimilable—be it in converting inactive into active modifications or vice versa or the production of one optical isomer instead of the other, or some other change of configuration, the consequence would be a different behavior toward the ferments, enzymes and sporozoa.
We now come to another feature which also may be of physiological interest, namely: the fact that the alkaloids largely used for therapeutical purposes, such as quinine, cinchonine, quinicine, conchinine, strychnine, brucine and morphia can, like micro-organisms, bi-part racemic forms. Thus cinchonine separates as salt from the inactive