THE LIVER AND THE SECRETION OF BILE 273 



far as the kidneys are concerned, we know indeed that certain diuretic substances 

 in the blood intensify the secretion of urine quite independently of the nervous 

 system. It is possible that the same thing 1 is true of the liver and that here, as 

 probably in the kidneys, the regulation of secretion is the result of a vasomotor 

 influence. However, this conclusion does not exclude the possibility of some 

 controlling influence by secretory nerves, for experience with the secretory nerves 

 of the stomach and pancreas teaches that the results of stimulation may be 

 entirely masked by various different circumstances. 



Although the secretion of bile goes on continuously, it shows certain varia- 

 tions which are not yet satisfactorily explained. Indeed the statements of 

 facts themselves exhibit a difference in many points, which is but little gratify- 

 ing. This much appears, however, from the observations at hand, that the 

 food exerts an important influence. The quantity of bile secreted is least in 

 fasting and declines steadily as the period is prolonged. The increase effected 

 by the food depends in the first place upon the kind : meat causing a consider- 

 able increase, carbohydrates causing little or none at all. 



Even in fasting the secretion of bile varies from hour to hour. After 

 feeding meat the rise mentioned above does not appear at once, but, as a rule, 

 only after the lapse of twenty to thirty minutes. The latent period is still 

 longer after feeding fat. Statements disagree as to when the maximum 

 occurs. 



This long latent period is of great importance for our theoretical con- 

 ception of the causes of the secretion, and seems to speak decisively for the 

 view that the increase results from an exciting influence of substances absorbed 

 from the alimentary canal, and that these substances act, therefore, directly 

 on the liver. Whether this view actually represents the truth of the matter, 

 or whether the increase in the secretion of bile which is to be observed after 

 feeding is due to a reflex effect upon vasomotor or secretory nerves, must for 

 the present be regarded as another open question. 



The direct stimulation of the liver by bile-producing (cholagogic) sub- 

 stances is illustrated further by the following facts to which Schiff first 

 directed attention. If both a biliary and an intestinal fistula have been 

 established in a dog, and the bile obtained from the former be injected into 

 the latter, or if ox bile be used for the same purpose, a considerable increase 

 in the amount of bile flowing from the biliary fistula is obtained. Schiff 

 explained these facts by saying that the injected bile was absorbed from the 

 intestine, came to the liver and was again secreted. 



We have direct proof of the correctness of this view in the fact that sheep's 

 bile, when injected into a mesenterial vein of a dog whose hepatic arteries have 

 been tied off, is secreted in the bile of th dog and can be demonstrated by the 

 spectroscopic test for cholohematin, which occurs normally only in the bile of 

 the sheep. At the same time the absolute quantity of bile rises. Bile or bile 

 salts given by the mouth have the same effect. The percentage content of solids 

 rises at the same time (Spiro and Voit). 



B. DEPENDENCE OF THE SECRETION OF BILE UPON THE BLOOD SUPPLY 



The supply of Hood to the liver manifestly influences the secretion of 

 bile to a considerable extent. If the general blood pressure be reduced mark- 



