IN BELATION TO ZOOLOGICAL DISTINCTION. 



33 



and among the former it is higher in birds than in mammals, which is in 

 accord with what we should expect. On the other hand, it is higher in the 

 horse than in the human being, notwithstanding the fact that the intensity 

 of the metabolic processes, as expressed by the intensity of oxidation per 

 kilo of body-weight, is lower in the horse than in man. Likewise do we note 

 an inverse relationship when we compare the dog and the guinea-pig, and 

 small and large birds. From this it is manifest that there must be some 

 factor or factors coupled with the relative blood-volume which compen- 

 sate for the discrepancies between the proportional volume and the rela- 

 tive degree of tissue activity. Such incongruities might in some instances 

 be accounted for in adaptations in the speed with which the total volume 

 of blood is forced through the vascular system, but the chief explanation 

 is doubtless to be found in differences in the composition of the blood, 

 especially as regards hemoglobin and other proteins. 



TABLE 9. Specific gravities of the blood as determined by different observers. 



If we compare the proportions of blood and the percentages of hemo- 

 globin and plasma proteins of the bloods of man and the frog, it will be noted 

 that the proportion of blood in the former, according to Welcker, is 7.69 



