26 HUMAN PHYSIOLOGY 



so-called myelin figures. It is soluble in ether and alcohol, 

 has the consistency of wax and yields imperfect crystals only 

 at a very low temperature. Boiled with acids and alkalies, 

 it splits up into fatty acid, phosphoric acid and cholin. 



Lecithin, no doubt partly united with proteid, is a con- 

 stituent of all animal cells. It is present in large quantities 

 in the brain, spinal cord, and yolk of birds' eggs. 



Protagon, a substance containing phosphorus and nitrogen 

 (constitution unknown), is a constituent of nerves and yields 

 similar decomposition products as lecithin. It can be extracted 

 from the brain by 85$ cold or 45$ warm alcohol and is thrown 

 down as crystals when cooled to o. It swells up in water, form- 

 ing an opalescent solution and is soluble only in warm alcohol and 

 in ether. At 50 C. it is decomposed, giving rise to the following 

 glucoside-like cerebrins free from phosphorus : cerebrin, homocere- 

 brin, encaphalin. The cerebrins, boiled with dilute sulphuric 

 acid, yield galactose and a fat called cetylid. 



Jecorin, a glucoside-like body containing phosphorus, appears 

 to be related to protagon. It is found in the liver and other 

 organs. 



The physiological significance of these substances is not known. 



To the fatty bodies also belong a few coloring compounds, 

 stored up in the body as pigments, called chromophane and lipo- 

 chrome. 



3. Proteids. The term proteid is here used in its widest 

 sense ; it also includes the proteid-like bodies (albuminoids) 

 which are not regarded as real proteids by many authors. 



(a) Composition of Proteids, 



Proteids all contain: carbon 50-55$, hydrogen 6.5-7.3$, 

 nitrogen 15-17$, oxygen 19-24$, sulphur 0.3-2.4$. 



Besides these, there are present phosphorus, iron, calcium, mag- 

 nesium, potassium and sodium; but these are not necessary con- 

 stituents of proteids, for they are united, either alone or with other 

 elements, to the already independent proteid molecule. 



Nearly all proteid bodies contain a small amount of mineral 

 constituents which, on incineration, remain behind as the ash. 

 These are not present as impurities, but are chemically united with 

 the proteid. 



Nothing is known for certain about the constitution, molecular 

 weight, and empirical formula of proteid. It is certain that the 

 proteid molecule is very large. 



