66 MANUAL OF PHYSIOLOGY. 



Glycocholic Acid, C 26 H 43 NO 6 , 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. 



2S H 43 N0 6 + H 2 = C 2 NH 5 2 + C n H 40 O 3 . 



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^HgoNPOg, is a complex nitrogenous fat found in 

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

 and yolk 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, ueurin, 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, C 160 H 308 N 5 PO 35 , is by some supposed to be the chief 

 constituent of brain substance, and by others said be a mixture 

 of the last two bodies. 



Neurin (O/to/m), C 5 H 16 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. 



Cholesterin, C 26 H H O, exists throughout the body where active 

 tissue change is going on, particularly the nervous centres. It is 

 a monatomic alcohol, and is the only one existing free in the body. 

 It may be obtained from gall-stones, some of which consist entirely 

 of cholesterin. It may occasionally be found in a crystallized form 

 in any of the fluids of the body normal or pathological, but it 

 only seems to be an effete product, nearly all that produced in the 



