28 MANUAL OF HISTOLOGY. 



5. Owing to a certain chemical inertness in fat, the latter appears 

 fitted for the formation of tissues which take but little active part in the 

 chemical processes of the economy. 



6. By the fermenting action of the protein compounds, but more by 

 contact with the oxygen of the atmosphere, the fats become decomposed, 

 and the fatty acids formed into other combinations, the final result of 

 which is the production of carbonic acid and water. The heat which 

 is evolved in this process constitutes them of the highest importance. 



7. According to Lehmann, the fats possess the nature of ferments, in 

 that with the protein compounds they lead to the generation of lactic 

 acid in fluids containing sugar and starch. The energy of pepsin in the 

 gastric juice is also said to be increased by the presence of fats. 



8. Though the neutral fats are not soluble in the watery fluids of the 

 body, their soapy combinations are, and are consequently of great im- 

 portance for the distribution of fatty acids through the system. 



The neutral fats are received into the body with food, although the 

 possibility of their production also in the human organism from hydro- 

 carbons must also be granted. That this takes place in many animals has 

 been proved, as is well known, by Liebig. Their origin from protein 

 compounds can likewise be no longer really doubted. 



20. 

 Cerebral Matters, Cerebrin and Lecithin. 



Among the substances of which the brain and spinal cord ar.e made up 

 ("but also in other parts of the animal body) there occur several peculiar, 

 unstable compounds, difficult of analysis. They are remarkable for the 

 property of swelling tip in hot water into a substance like starch, for 

 their solubility in warm alcohol and ether, and for their occasionally 

 containing phosphorus. They were formerly erroneously designated as 

 phosphorous fatty matters. 



Cerebrin, C, 7 H 3S ]Sr0 8 . 



Cerebrin, originally described by Fremy as cerebric acid, and after- 

 wards investigated by Gobley and Miiller, is a white powder, seen under 

 the microscope to be composed of roundish globules. It can only be dis- 

 solved in warm alcohol and ether, and is decomposed by boiling hydro- 

 chloric and nitric acids. It is insoluble in ammonia, caustic potash, 

 and baryta water, and also in cold water ; while in hot, as already men- 

 tioned, it swells up into a substance resembling boiled starch. 



On being boiled with acids, cerebrin yields a species of sugar, and is 

 therefore a glucoside. Its precise nature remains for further investiga- 

 tion. 



Lecithin, C 42 H 84 NP0 9 . 



This substance, first discovered by Gobley, is indistinctly crystalline. 

 It resembles wax, may be easily melted, and is soluble in hot alcohol 

 and ether. It enters into combination with acids and salts. In warm 

 water it gelatinizes like cerebrin. 



Lecithin is a substance easily decomposed. By prolonged boiling in 

 spirits of wine, or better still, in acids or bases, as baryta water, it 



