IN RELATION TO ZOOLOGICAL DISTINCTION. 



49 



in the guinea-pig 2.59 : 1, in the rabbit 1.33 : 1, and in the dog 4.41 : 1. 

 While undoubtedly not only the percentages but the ratios are variable 

 under both normal and abnormal conditions, the differences are such as 

 to imply positive zoological distinctions. A serious inquiry into the zoologi- 

 cal peculiarities of leucocytes will probably yield important results. 



TABLE 18. The percentages of different varieties of leucocytes in the bloods 



of different species. 



Finally, studies of immunity against infectious diseases show clearly 

 that natural immunities of different species are owing to specific physio- 

 logical peculiarities of the individual's leucocytes. "The dominant feature 

 of the phenomena exhibited in natural immunity against microorganisms," 

 writes Metchnikoff (Immunity in Infective Diseases, trans, by Burnie, 

 1905, 206), "is represented by the phagocytic reaction observed through- 

 out the animal series that is exercised against parasites belonging to all 

 the microbal groups. Phagocytosis is exhibited not only by the macro- 

 phages, but also in a high degree by the microphages which stand out as 

 the defensive cells par excellence against microorganisms. The action is 

 divided into series of vital physiological acts, such as sensitiveness to the 

 microorganisms and their products, amoeboid movements which serve to 

 ingest the microorganisms, and into chemical and physico-chemical pro- 

 cesses, such as the destruction and digestion of the devoured organisms. The 

 phagocytes enter into a struggle against the microorganisms and rid the 

 animal organism of them without requiring any previous help on the part 

 of the body-fluids. Phagocytosis exercised against living and virulent 

 microorganisms is sufficient to insure natural immunity." 



THE PROPORTION OF CORPUSCLES TO SERUM IN RELATION TO GENERA. 



According to Welcker (loc. cit.), the proportion of corpuscles to serum 

 is higher in warm-blooded than in cold-blooded animals ; higher in mammals 

 than in birds ; higher in birds than in the amphibia and fish ; higher in the 

 "scaly" amphibia than in the "naked" amphibia, and lowest in fish. His 

 figures indicate that in mammals, birds, and amphibia the corpuscles repre- 

 sent from about one-third to one-fourth of the blood, and in fish only about 

 one-fourteenth of the blood. His figures for mammalian blood are, in the 

 light of subsequent investigations, too low, the mean as shown by Abder- 

 hal den's analyses (Zeit. f . physiolog. Chemie, 1897, xxm, 521 ; 1898, xxv, 65) 

 being nearly 40 per cent; in fact, it is only in certain of the ruminants that 

 we find so low a standard as that given by Welcker (tables 19 and 20). 



