The importance attached to matters secreted by pathogenic microbes is constantly on the increase. As a result pathologists now attribute to the secretions the greater portion of the effects which minute organisms produce.
From a purely physiological standpoint microbian products may be divided into the three following groups: 1. Those which exert upon the economy a poisonous influence, and upon which the virulent properties of the microbe depends. 2. Those possessing a vaccinating power; they confer immunity not by accumulating in the tissues but by passing through them and modifying the dynamic power of cells and the chemical qualities of the fluids and tissues. Finally, a third group, which, though themselves non-pathogenic, diminish the power of resistance of the organism to the attacks of other pathogenic varities; and even render forms non-pathogenic virulent.
The effects upon the system of the different products secreted by these microscopic forms have been very