BLOOD. 161 



existence, under tlie most opposite kinds of food, we find that 

 the bile is a secretion of the liver; whilst amongst all the 

 higher classes of animals and many of the lower, urea and nric 

 acid, or one of the two, occur as a constant secretion of the 

 kidney. 1 It seems opposed to all reason to imagine that in 

 animals as difterent in structure as they are opposite in their 

 habits of life, and under every possible variation of circum- 

 stances, these fixed and definite compounds should be products 

 of the metamorphosis of the plasma during the nutrition of 

 every form of tissue. It is, however, easy to conceive that the 

 corpuscles which, although diff'erent in their form, are similar, 

 if not identical, in their chemical constitution, in the blood of 

 all these animals, should, under similar conditions, yield similar 

 products as the result of their metamorphosis, and that these 

 products should take the form of urea, uric acid, and bilin. 

 This consideration alone is deserving of much weight in sup- 

 port of the view that I am now advocating. If the urea, uric 

 acid, and bilin were formed in accordance with the other hypo- 

 thesis, their production would be increased, diminished, or 

 stopped, according as nutrition was proceeding favorably, was 

 deficient, or was entirely checked, as happens in certain dis- 

 orders. But it is well known that the production of these 

 substances is by no means dependent on such circumstances. 

 The secretion of urea, uric acid, and bile proceeds, both in man 

 and animals, when the tissues are gradually wasting from dis- 

 ease, and when their nutrition is utterly suspended ; they are 

 separated long after the body has ceased to take any food what- 

 ever, in fact, as long as respiration and even life itself remains, 

 the only necessary condition being the healthy state of the 

 secreting organs. I have had several opportunities of examining 

 the urine during inflammatory diseases, both before and during, 

 or shortly after the height of the attack, and have found that, 

 in the latter case, there was always a greater amount of urea 

 than in the former. This is easily explained by the conside- 

 ration that the active metamorphosis of the blood-corpuscles is 

 accelerated by an excited inflammatory state, and that, conse- 

 quently, a larger number of the corpuscles is consumed during 

 a given time, than in the ordinary condition of the system. 



Muller's Handbuch tier Physiologic, vol. 1, pp. 515 and 588. 



11 



