594 OF SECRETION AND EXCRETION. 



nation of urea, as a necessary means of removing from the blood those products 

 of the disintegration of the tissues, which are taken back into the circulation 

 even when the life of the being is most purely vegetative ; and this neces- 

 sity arises from that limitation to the existence of each individual part, which 

 is most remarkable when the processes of growth and development are taking 

 place with the greatest rapidity. 



633. If, now, we bring together all the facts at present known, with regard 

 to the actions performed by the Liver, they appear to justify the following con- 

 clusions with respect to its offices. 1. That the Liver is essentially an organ 

 of excretion, designed to remove from the Blood those hydrocarbonaceous pror 

 ducts of the disintegration of the tissues, which cannot be converted into sugar 

 or fat so as to be prepared for direct elimination by the respiratory organs. 2. 

 That in doing this, it converts these excrementitious matters into the glyco- 

 cholic and tauro-cholic acids; substances which have a certain utility in the 

 digestive process, and which, after ministering to that function, are capable of 

 being reabsorbed, and of undergoing oxidation; whereby the greater part of 

 their components are carried off in the form of carbonic acid and water by the 

 lungs, the remainder (chiefly the alkaline bases, with the sulphur of the taurine, 

 which is converted into sulphuric acid) being eliminated by the kidneys. 3. 

 That not only by the separation of biliary matter from the blood and by the 

 operation of this upon the alimentary substances, but also by the change in the 

 constituents of the blood itself, the Liver aids in preparing materials for the 

 combustive process. For it converts all forms of saccharine matter derived from 

 the food into " liver-sugar," the form which is most favorable to oxidation ; and 

 it would seem capable also of generating this sugar from protein-compounds, or 

 from certain products of their decomposition ( 46). And it exercises a similar 

 transforming power upon fatty matter; generating the peculiar " liver-fat," 

 either from other oleaginous or from saccharine substances supplied by the food, 

 or, as it would also appear, from protein-compounds, or from the products of the 

 early stages of their retrograde metamorphosis ( 40). In all the foregoing 

 actions, the Liver is subservient to the Respiratory function ; but in a mode 

 very different from that formerly propounded by Prof. Liebig, 1 who represent- 

 ed the Liver as destined to prepare by secretion the materials adapted for the 

 sustenance of the combustive operation. For it is quite certain that if the 

 whole of the solid biliary matter poured into the intestine were reabsorbed, it 

 could furnish but a small proportion (probably not more than one-twelfth) of 

 the total amount of hydrocarbon which is eliminated by the lungs ; and the pre- 

 paration of the liver-sugar and liver-fat in the blood itself is evidently the far 

 more important part of the office of the Liver as regards the Respiratory func- 

 tion. 4. But the Liver also aids, if the statements of M. Bernard on this point 

 be correct, in the assimilation of the histogenetic materials, which have been 

 newly absorbed from the digestive cavity ; the raw albumen being converted by 

 its means into a form more suitable for transmission through the system in the 

 current of the circulation, and even fibrin being generated at its expense ( 167, 

 169). It must be admitted, however, that there are many points in the func- 

 tion as well as in the structure of the Liver which still remain to be cleared up. 



3. The Kidneys. Secretion of Urine. 



634. The Kidneys cannot be regarded as inferior in importance to the Liver, 

 when considered merely as excreting organs ; but their function only consists 

 in separating from the blood certain effete substances which are to be thrown off 

 from it, and has no direct connection with any of the nutritive operations con- 



1 "Chemistry applied to Animal Physiology," 1842. 



