204 or THE BLOOD. 



bonic acid which is one of the products of their disintegration shall be conveyed 

 away. And this view is in complete harmony with the fact that the proportion 

 of Red corpuscles in the blood bears a close relation to the amount of Respira- 

 tory power (as shown in the quantity of carbonic acid set free, and in the 

 amount of heat generated) in different classes of Vertebrata; both being great- 

 est in birds, nearly as great in Mammals, very low in most Reptiles, and vary- 

 ing considerably among Fishes. 1 Again, we observe that among Carnivorous 

 Mammalia, the proportion of red corpuscles is considerably greater than it is 

 among the Herbivorous tribes, whose nervo-muscular energy is (upon the whole) 

 so greatly inferior; and it is in the condition of greatest animal vigor, in the 

 Human system, that we find their amount the greatest, whilst the reduction of 

 that vigor by chronic disease of any description seems invariably attended with 

 a more marked diminution in this constituent of the blood than in any other. 

 And in those Anaemic states of the system, in which the proportion of red cor- 

 puscles is reduced to an extremely low point ( 174), we invariably find that the 

 animal powers are correspondingly depressed ; the capacity for sustained exer- 

 tion, either of the mental faculties, or of the motor apparatus, being almost 

 destroyed, although both the nervous and muscular systems are very easily ex- 

 cited to feeble action. However difficult it may seem to explain, on this view, 

 the persistence of any degree of nervo-muscular power, in such cases as that 

 already referred to, in which the Red corpuscles appeared to be entirely defi- 

 cient ( 176), the same difficulty attends any attempt to assign a use for them 

 which shall be in accordance with their well-marked importance as constituents 

 of the Blood. And we may suppose that, in such cases, the Colorless corpuscles, 

 although discharging their duty less perfectly, might to a certain extent perform 

 it, as they seem to do among the Invertebrata. 



195. The difficulty 'of precisely determining the functions of the Red cor- 

 puscles is even surpassed by that of assigning the probable duty of the Color- 

 less. The considerations already adduced appear to show that the Colorless 

 corpuscles are to be considered as cells of a lower grade than the Red; since 

 they represent them among Invertebrated animals, and also in the incipient 

 blood of Vertebrata; and also, because cells resembling the former (if not the 

 very same) pass on to develop themselves into the latter ( 155). Still we 

 find that this final change does not occur among the Invertebrata ; and it is 

 obvious, therefore, that even in their colorless state the corpuscles have a 

 function to discharge in the vital economy. Little light has yet been thrown 

 upon this subject by inquiry into the Chemical composition of the blood-cor- 

 puscles of the lower animals ; and no means have yet been devised for obtain- 

 ing the colorless corpuscles of the higher in a separate state, for the purpose of 

 determining this. A minute sample of the blood-corpuscles of a Crab, however, 

 examined by Prof. Graham, has been found by him to contain "a sensible quan- 

 tity of iron, the proportion being perhaps as large as in red corpuscles/' 3 Thus, 

 then, we have evidence that the difference of hue between the two sets of Cor- 

 puscles does not involve any considerable difference in the proportion of one of 



1 "Princ. of Phys., Gen. and Comp.," $ 619, Am. Ed. Among invertebrated animals, 

 as a general rule, the degree of nervo-muscular energy that can be put forth, the 

 quantity of carbonic acid produced in respiration, and the amount of heat generated in 

 the body, are alike at a low standard ; and the fluid constituents of the blood, with the 

 colorless corpuscles that float in it, would seem to convey oxygen to the tissues, and car- 

 bonic acid to the respiratory organs, with sufficient facility. In Insects, however, the 

 case is different; the nervo-muscular activity, capacity of respiration, and heat-producing 

 power being all extraordinarily high. Their want of red corpuscles would here seem to 

 be compensated, so far as the respiratory process is concerned, by the introduction of air 

 through the tracheal apparatus, into the tissues themselves. ("Princ. of Phys., Gen. 

 and Comp.," \ 620, Am. Ed.} 



2 "Philosophical Transactions," 1846, p. 105. 



