222 CIRCULATING FLUIDS : 



tion, since tliey are produced in fasting persons, and even when 

 nearly all the soft tissues are wasted away. 



We do not, however, intend to assert that nutrition exercises 

 no influence over these products, or that the peculiar structure 

 of each secreting organ is not to be considered. Neverthe- 

 less I cannot agree with certain physiologists who maintain 

 that in granivorous animals, sugar formed in the chyle is the 

 cause of the carbonic acid evolved from the lungs, or that urea, 

 lu-ic acid, and bilin are formed solely from the albumen, and 

 that the blood-corpuscles take no part in this action ; for the 

 uniform and simultaneous formation of carbonic acid, urea, 

 uric acid and bilin, in animals whose food is so varied, and whose 

 habits and conditions of life are so diversified, renders it pro- 

 bable that these substances are simultaneously formed, as a 

 consequence of one and the same metamorphic act. On the 

 other hand, we must not omit to notice that the occurrence of 

 the non-nitrogenous hippuric acid in the ruminantia, the ex- 

 cessive production of uric acid accompanied frequently with a 

 total absence of urea in bii'ds and amphibia, and the inverse 

 ratio in which these substances occur in man, monkeys, &c., 

 as likewise the different chemical relations of the bile in fishes 

 and amphibia, point out the influence of nutrition and of the 

 organization in general on these secretions. What is the ultimate 

 piu'pose of the blood-corpuscles in the organism if they do not 

 participate in the formation of these products, and if they ex- 

 perience no real material change ? The idea that the nutrition 

 of the tissues is accomplished by the aggregation of blood- 

 corpuscles is now abandoned, and the supposition that these 

 molecules exert a vitahzing influence on the organized tissues 

 is perfectly unintelligible. I can form no conception of a 

 blood-corpuscle that is not undergoing a continuous material 

 change, and I regard this change as the ultimate object of its 

 existence. 



Daily experience shows us that the fluids which are secreted 

 by the principal glands take their origin from the blood: the 

 question then arises whether these secretions exist in the blood 

 itself, that is to say, whether the blood which enters a secreting 

 organ, as the kidney or liver, indicates a difl'erence of composi- 

 tion as it leaves that organ. At first sight we should doubt- 

 less answer this question in the affirmative; but taking into 



