450 EXCRETION. 



rendered dark by the action of the acid, and the sugar itself will be acted upon, even if 

 no bile be present, but the color due to the sugar alone is yellow. The peculiar play of 

 colors above described can easily be recognized after a little practice, and is observed 

 only in the presence of the biliary salts. 



The ordinary modifications in the application of this test are unimportant. Some 

 recommend to add the sulphuric acid first, and then to add the solution of sugar; and 

 some, after adding to the liquid two-thirds of its volume of sulphuric acid, drop into the 

 mixture one or two lumps of cane-sugar. The reaction with the biliary salts is essen- 

 tially the same, whichever of these methods be employed. 



Excretory Function of the Liver. 



In 1862, in studying the properties and physiological relations of cholesterine, we 

 gave the first definite account of an excretory function of the liver. The experiments and 

 observations upon which we based our conclusions were extended and laborious, and, as 

 far as we know> they have not been repeated in detail by other observers; but the results 

 must be taken as positive, if the accuracy of the experiments be admitted, and they have 

 been adopted, to a greater or less extent, by scientific authorities. The details of these 

 experiments are too elaborate to be given in full, as contained in the original memoir. 1 



The few statements with regard to the function of cholesterine to be found in works 

 published before 1862 are very indefinite. In most treatises on physiology, this substance 

 is hardly mentioned, it being generally regarded as a curious principle, interesting only 

 to the physiological chemist. We have given, in the memoir referred to, extracts from 

 the works of Carpenter, Lehmann, Mialhe, and Dalton, which contain all that is said 

 with regard to the probable function of cholesterine ; and these quotations, which embody 

 about all that we could find on the subject, show that its office was not in the least 

 understood. Inasmuch as cholesterine is the only excrementitious principle as yet dis- 

 covered in the bile, bearing the same relation to this fluid that urea does to the urine, it is 

 evident that the ideas of physiologists, with regard to any excretory function of the liver, 

 must have been very indefinite before the relations of cholesterine had been determined. 



The first question which arises is whether the liver has any excretory function. Some 

 authors have assumed that the bile is purely excrementitious and has no function as a 

 secretion. This question we have fully discussed in connection with the subject of diges- 

 tion. The confusion that has arisen with regard to this point has been due to the fact 

 that those who adopted the view that the bile was simply an excretion denied to it any 

 digestive properties ; while, on the other hand, those who believed it to be concerned in 

 digestion would not admit that it was an excretion. We have shown conclusively, in 

 treating of intestinal digestion, that the bile is so important in this process as to be essen- 

 tial to life ; but we have shown, at the same time, that the liver eliminates from the 

 blood one of the most important of the products of disassimilation. It will be found 

 important, as bearing upon the probable function of the bile, to apply to this fluid the 

 general law of the distinctions between secretions and excretions. 



Cells of glandular epithelium are constantly manufacturing, out of materials furnished 

 by the blood, the elements of the true secretions ; but these elements do riot preexist in 

 the blood, they appear de novo in the secreting organ, and they never accumulate in the 

 system when the function of the secreting organ is disturbed. Again, the true secretions 

 ara not discharged from the body, but they have a function to perform in the economy, 

 and are poured out by the glands intermittently, at the times when this function is called 

 into action. As far as the biliary salts (the taurocholate and glycocholate of soda) are 

 concerned, the bile corresponds entirely to the true secretions. These principles are 

 manufactured by the liver, they do not preexist in the blood, and they do not accumu- 



1 FLINT, Jr., Experimental Researches into a New Excretory Function of the Liver. American Journal of 

 the Medical Sciences, Philadelphia, 1862, New Series, vol. xliv., p. 305, et seq. ; and, Reclierches efcperimentales sur 

 um, nouvelle fonction dufoie, Paris, 1868. 



