IN RELATION TO ZOOLOGICAL DISTINCTION. 47 



birds' blood is relatively large and the volume of serum small ; while in the 

 case of cold-blooded animals the opposite seems to be true. Sheep's blood 

 yields a larger volume of serum than the bloods of most other mammals. 



Then again the fibrins of the bloods of different genera are by no 

 means identical. Fermi states that pig's fibrin is dissolved in a 0.5 per cent 

 solution of HC1 in as many hours as the fibrin of bullock's blood is in as 

 many days. He also notes that the solubilities of the fibrins of the pig, 

 sheep, horse, and bullock in dilute vegetable and mineral acids differ in 

 the order given, the highest solubility being in the fibrin of the pig and 

 lowest in that of the bullock. 



Another generic distinction is shown in the fact that commercial pep- 

 tone when injected into the circulation of the dog renders the blood non- 

 coagulable, while it is without effect on the blood of the rabbit. 



Finally, the studies of Leo Loeb (Archiv f. path. Anat. u. Phys., 1903, 

 CLXXIII, 35, 113; and 1904, CLXXVI, 10; Hofmeister's Beitrage, 1904, v, 133) 

 on the phenomena of coagulation in both warm- and cold-blooded animals 

 have demonstrated marked zoological peculiarities. In these comparative 

 studies he has found not only that the relations between the blood plasma 

 and the tissue extracts (tissue-coagulins) are specific in so far as different 

 fibrinogens or different tissue-coagulins are chemically different, but that 

 tissue-coagulins and fibrinogens show a specific adaptation to each other. 

 The tissue-coagulin of one class of animals causes a more rapid coagulation 

 of the plasma of the same class than of the plasma of another class. The 

 demonstration of this specific adaptation could be more easily accomplished 

 in some classes of animals than in others. It is very marked in inverte- 

 brates; but even here the specificity is not absolute; it is a relative, gradu- 

 ated, specific adaptation. The substances of related species are active, but 

 not so active as the substances of the same species. 



In vertebrates with nucleated red blood corpuscles and stable blood 

 plasmas, the relative specific adaptation is likewise easily demonstrable. 

 It is present in the case of the mammalian blood and tissues, but here it 

 can not be demonstrated as clearly. Mammalian blood can not be kept 

 liquid outside the body as easily as that of other animals, and in mammalian 

 blood either the number of factors causing coagulation is greater than in 

 the case of other classes, or one single factor is preponderating to such a 

 degree that the specific adaptation of the tissue-coagulins to the fibrinogen 

 becomes somewhat obscured. The relations between tissue-coagulins and 

 plasma are similar to those of the artificially produced immune bodies to 

 their antigens. Sometimes non-specific tissue-coagulins are admixed with 

 the specific ones. A specificity of the thrombins exists in so far as the 

 thrombins of different classes are different (Bordet et Gengou), but a 

 specific adaptation can not be shown to exist in their case. 



THE LEUCOCYTES OF THE BLOODS IN RELATION TO GENERA. 



The leucocytes of vertebrates contain iron as a normal constituent, 

 but Boyce and Herdman (Philosoph. Trans., 1897, LXII, 34) have found 

 copper in place of iron in the leucocytes of the oyster. Huppert (Centralb. 



