EXCKETORY ACTION OF THE LIVER. 405 



ing albumen is what is known as Pettenkofer's test : To the suspected 

 liquid are added a few drops of a strong solution of cane-sugar. Sulphuric 

 acid is then slowly added, to the extent of about two-thirds of the bulk of the 

 liquid. It is recommended to add the acid slowly, so that the temperature 

 shall be but little raised. If a large quantity of the biliary salts be present, 

 a red color shows itself almost immediately at the bottom of the test-tube, 

 and this soon extends through the entire liquid, rapidly deepening until it 

 becomes dark lake or purple. If the biliary matters exist in very small pro- 

 portion,'" it may be several minutes before a red color makes its appearance, 

 and the change to a purple is correspondingly slow, the whole process occu- 

 pying fifteen to twenty minutes. 



EXCRETORY ACTION OF THE LITER. 



Although the liver produces a greater or less quantity of urea, this sub- 

 stance is discharged from the body chiefly in the urine and mere traces exist 

 in the bile. The excretory action of the liver will be considered, in this con- 

 nection, with reference to the bile itself. At the present day it is generally 

 admitted that the bile is an excretion as well as a secretion ; and this ques- 

 tion has been fully discussed in connection with the physiology of digestion. 

 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 excre- 

 tion. It will be useful, as bearing upon the probable office of the bile as an 

 excretion, to apply to this fluid the general law of the distinctions between 

 secretions and excretions. 



Cells of glandular epithelium are constantly forming, out of materials 

 furnished by the blood, the characteristic constituents of the true secre- 

 ions ; but these do not pre-exist in the blood, they appear first in the secret- 

 ting organ, and they never accumulate in the system when the action of the 

 secreting organ is disturbed. Again, the true secretions are not discharged 

 from the body, but they have an office to perform in the economy, and are 

 poured out by the glands intermittently, at the times when this office is called 

 into action. As far as the biliary salts, sodium taurocholate and sodium 

 glycocholate, are concerned, the bile corresponds entirely to the true secre- 

 tions. These salts are formed in the liver, they do not pre-exist in the blood, 

 and they do not accumulate in the blood when their formation in the liver is 

 disturbed. The researches of Bidder and Schmidt and others have shown 

 that although the biliary salts can not be detected in the blood or chyle 

 coming from the intestine, they are not discharged in the faeces. These facts 

 point to an important office of the bile as a secretion. It is true that the 

 bile is discharged constantly, but during digestion its flow is very much more 

 abundant than at any other time. It is pretty well established that during 

 the intervals of the flow of the secretions, the glands are forming the materi- 

 als of secretion, which are washed out, as it were, in the great afflux of blood 

 which takes place during what has been called the activity of the gland. 



