CHEMICAL PHYSIOLOGY. 19 



the composition 5 H 15 N0 2 . It is closely related to 

 neurine, C 5 H 13 N, a base obtainable, together with 

 choline, from cerebric acid or lecithine, and we are 

 justified in assuming that it is derived from the de- 

 composition of that body. Lecithine consequently 

 may be considered as a normal ingredient of bile. 



The biliary acids yield a particular test, called, after 

 its discoverer, Pettenkofer's reaction. When mixed 

 with sugar and sulphuric acid they produce a splendid 

 purple colour. It has been found that other acids, 

 such as lithofellic, also yield this test ; and I found, 

 further, that cerebric acid yielded it with rare in- 

 tensity. I therefore applied the spectroscope, and was 

 glad to discover some means for the distinction of the 

 various acids in the coloured test solution. The biliary 

 acids show two bands, cerebric acid and vitelline only 

 one. These spectra are, however, difficult to observe, 

 and require sunlight or oxhydrogen light for their 

 complete development. 



The quantity of bile secreted in the human body in 

 a day has been estimated at 1200 grammes, or the 

 bulk which would fill a wine bottle and a half. Con- 

 clusions from quantities observed in animals can only 

 be used with caution, as some animals, e. g., the guinea- 

 pig, produce enormous quantities of bile relatively to 

 their body weight, while dogs and sheep produce 

 relatively small quantities. The production is more 

 likely to stand in proportion to the size and weight of 

 the liver (hitherto neglected as a physiological factor) 

 than to the weight of the body, to which hitherto 

 quantities were almost exclusively referred. 



