74 MANUAL OF PHYSIOLOGY. 



violet color produced by cane sugar and sulphuric acid at a tem- 

 perature of about 70 C. (Pettenkofer's reaction). 



Taurocholic Acid, C 26 H 45 NSO7, is most plentiful in the bile of 

 carnivora, where it occurs combined with soda. It is decomposed 

 by prolonged boiling with water into taurin and cholic acid, 

 thus : 



TatirochoHc acid. Taurin. Cholic acid. 



C 26 H 45 NS0 7 + II 2 = C 2 H 7 NS0 3 f C 24 H 40 5 . 

 Glycocholic Acid, CaeH^NOe, found in the bile of herbivora and 

 man. It crystallizes in fine white, glistening needles. It exists 

 as the glycocholate of soda in the bile. By boiling with weak 

 acid it yields glycin and cholic acid. 



Glycocholic acid. Glycin. Cholic acid. 



C 26 H 43 N0 6 + H 2 = C 2 NH 5 2 + C 24 H 40 5 . 



In the bile certain matters also exist to which the color is due, 

 the principal being bilirubin in man and carnivora, and biliverdin 

 in herbivora. They are probably derived from the coloring mat- 

 ter of the blood. They can be recognized by treating the solution 

 with nitric acid which is colored with red fumes, when a play of 

 colors ending in a dull purple is seen. 



Lecithin, C 44 H 90 NP0 9 , is a complex nitrogenous fat found in 

 most tissues and fluids of the body, particularly in the nerve tissues 

 and yelk of egg. It is an interesting product of decomposition of 

 the constituents of the brain, which is related in constitution to 

 the neutral fats, and it may be regarded as an acid glycerin ether. 

 It is easily decomposed when heated with baryta water, splitting 

 into glycerin, phosphoric acid, neurin, and barium stearate. 



Another body called Cerebrin, not containing any phosphorus 

 and of doubtful composition, can be obtained from brain sub- 

 stance, and is also found in nerve fibres and pus corpuscles. It 

 is a light colorless powder which swells in water. 



Protagon, Ci 60 H. ws N ^PO-^, is by some supposed to be the chief 

 constituent of brain substance, and by others said to be a mix- 

 ture of the last two bodies. 



Neurin (Cholwi), C 5 Hi 5 NO 2 , is an oily liquid only found in the 

 body as a product of the decomposition of lecithin, but it has 

 been obtained synthetically. 



