678 INTERNAL SECRETIONS AND PRESERVATION OF LIFE. 



ther emphasized by the following lines, also quoted from Metch- 

 nikofFs text, that is to say, as interpreted by his translators: 

 "The sponges are ..of such undifferentiated organization that 

 they were long considered to be colonies of protozoa, consist- 

 ing like the protospongia, of separate flagellated and amoeboid 

 individuals. Later on, it was however ascertained that they 

 bore a certain relationship to the polyps and their allies (coelen- 

 terata)." . . . "There are a few species, such as the 

 siphonochalina coriacea, whose mesodermic cells alon3 inclose 

 all foreign bodies; so that the cylindrical cells of the endo- 

 derm merely serve to keep up the continuous passage of 

 the fluid through the sponge. The phagocytes of both layers 

 have the power of rejecting insoluble matters, which collect in 

 the larger efferent canals/' . . . "We are, however, chiefly 

 concerned here with the fact that the mesodermic phagocytes 

 are able to digest the substances as well as to inglobe them, and 

 to reject the insoluble residue." 



The nature of the digestive process has, however, remained 

 obscure. "The bacilli which have been inglobed by leucocytes," 

 continues Metchnikoff, "are much more rapidly digested in the 

 case of mammals that are either naturally refractory, as the 

 dog and fowl, or have been rendered artificially immune against 

 anthrax by vaccination, as the rabbit. This fact is shown by 

 the researches of Hess, as well as my own. It is easy to follow 

 the digestion of many other microbes within the leucocytes. 

 Vacuoles are often seen to form around the bacteria that have 

 been swallowed, just as we have noticed in the digestion of 

 nutrient material by the protoplasm of the protozoa and the 

 myxomycetes. I have been able to observe the changes under- 

 gone by the spirilla of recurrent fever in the leucocytes of 

 monkeys, as well as those undergone by the vibrio septica3miae 

 in the leucocytes of immunized guinea-pigs, and those by ery- 

 sipelas streptococci in the leucocytes of man, etc. We are at 

 present ignorant of the precise manner in which this digestive 

 and destructive action is accomplished, and do not even know 

 whether the substance which kills the microbes is a ferment 

 or not." 



Before submitting this question to analysis the manner 

 in which the products of digestion, both the nutritional ele- 



