EXCHANGE OF MATERIAL. 33 



heating trimethylamine and ethylene oxide in aqueous solution (N (C H 3 ) 3 + 

 C a H 4 O + II., O = Neurin). Glycero-phosphoric acid (C 3 H 9 PO 6 or 

 C 3 H 7 O 3 PO (OH) 2 ), the product which is obtained when phosphoric anhy- 

 dride or glacial phosphoric acid acts on glycerine, is a syrupy body, soluble in 

 water not in alcohol. Taking up H 2 O, it splits readily when warmed into 

 glycerine and phosphoric acid. Along with Neurin and a fatty acid, it is a 

 product of the decomposition of Lecithin, a body which may be regarded as 

 glycero-phosphoric acid in which H 2 O is replaced by Neurin, and 2 atoms of 

 H in the radical by 2 atoms of stearyl (C 18 H^ O). Lecithin is consequently 

 called Neurin-distearyl-glycero-phosphate. Lecithin is an imperfectly crystal- 

 lizable body which fuses readily, is soluble in ether and swells out in water, like 

 starch, without dissolving. It is obtained by treating the ether alcohol 

 extract of yolk of egg, after first freeing it. from fats, with alcoholic solution 

 of platinic chloride. A chloride of platinum and of Lecithin separates, of 

 which the ethereal solution, when decomposed by sulphuretted hydrogen, 

 yields Lecithin hydrochlorate as a wax-like mass. The alcoholic solution of 

 this substance, when poured into boiling baryta water, splits into glycero- 

 phosphate, Neurin and stearate. Bodies of similar constitution in which the 

 radical of stearic acid is replaced by that of palmitic or of oleic acid are also 

 called Lecithins. 



Cholesterin (C 26 H^ O) crystallizes readily from ether-extract of powdered 

 gall-stones (of which it is usually the chief constituent) in rhombic plates, 

 which in mass have a mother-of-pearl lustre. These crystals contain a mol. 

 of H 2 O, which they lose at 100 C. It fuses at 145 C., is insoluble in water, 

 soluble in alcohol, ether, chloroform, &c. When evaporated with nitric acid, 

 the residue on the addition of ammonia acquires a dull red colour. If sulphuric 

 acid is added to its volume of solution of cholesterin in chloroform, the solution 

 becomes first red then purplish, while the subjacent layer of acid acquires a 

 distinct green fluorescence. A body resembling Cholesterin (Excretin) has 

 been discovered by Marcet in human faeces, to which the formula C 20 H 36 O is 

 now attributed. 



Cerebrin is a body of imperfectly known constitution, which is distinguished 

 from Lecithin with which it is associated by its solubility in boiling absolute 

 alcohol, its insolubility in cold alcohol, and its not being decomposed or acted 

 upon by boiling baryta water. 



EXCHANGE OF MATERIAL. 



The term "exchange of material" is used to denote the 

 results of the chemical processes (" functions"), which con- 

 stitute the life of the animal body, as they exhibit them- 

 selves in the entrance and discharge of material at its 

 surface. Its total amount is known by the direct or 

 indirect measurement of the quantities of carbon and 



D 



