CHAPTER II. 



SPECIFICITY OF THE BLOOD OF VERTEBRATES IN RELATION 

 TO ZOOLOGICAL DISTINCTION. 



A large number of facts bearing upon generic and allied differences of 

 the blood are scattered throughout the voluminous literature of the bio- 

 logical sciences, but these with few exceptions as isolated facts seem to 

 be of so little importance as not to attract more than passing notice. When, 

 however, they are considered collectively and in connection with the pecu- 

 liarities pointed out or suggested in the preceding chapter, and with our 

 discoveries of the specific peculiarities of the hemoglobin crystals shown 

 in subsequent chapters, they will be found to be so positive in their mean- 

 ing as to leave no doubt that we are on the threshold of a specialization so 

 sensitive as to justify the prediction that the blood of each family, genus, 

 species, and individual will be found to be absolutely specific. While it has 

 not been possible for us to make an exhaustive collection of such data, we 

 have brought together sufficient in the following paragraphs to show clearly 

 that we may not only generalize but also specialize, and that with a number 

 of determinant facts and with the present progress of research we are fast 

 approaching the time when not only genera and species but also races, 

 and even individuals of a race or species, can with as much or with greater 

 certainty be distinguished by the peculiarities of their bloods as by the 

 conventional methods of the zoologist. Moreover, we believe, from even 

 the limited studies we have made, that the zoological distinctions indicated 

 by peculiarities of the blood will be found to be paralleled by similar 

 peculiarities of other of the more important body fluids and solids. 



THE QUANTITY OF BLOOD IN RELATION TO BODY-WEIGHT IN 

 REFERENCE TO GENERA. 



The investigations of Welcker and others show that, while the pro- 

 portions of blood to body-weight in both warm-blooded and cold-blooded 

 animals, excepting certain of the amphibia and fishes, do not as a rule vary 

 greatly, the differences in the various orders, classes, etc., are of zoological 

 significance. 



The methods of estimation are not exact, so that the figures recorded 

 are to be regarded as being approximate. The discrepancies in the records 

 of different observers in the proportions in members of a given species are 

 to be accounted for in a measure in this way, and in part in variations due 

 to age, sex, general condition, and the changes that arise from various 

 incidental normal and abnormal states. Notwithstanding the crudity of 

 the methods generally, the records are sufficiently in agreement to indicate 

 specific but not important zoological distinctions. 



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