CHEMIC COMPOSITION OF THE HUMAN BODY. 23 



(b*) Mucoids. The mucoids resemble the mucins though differ- 

 ing from them in solubility and in not being precipitable 

 from alkaline solutions by acetic acid. They are found in 

 the vitreous humor, white of egg, cartilage, and in other 

 situations. They differ slightly one from the other in proper- 

 ties and chemic composition. They yield on decomposition a 

 carbohydrate. 



3. NUCLEO-PROTEIDS. 



The nucleo-proteids are obtained from the nuclei and cell-substance 

 of tissue-cells. Chemically they are characterized by the presence of 

 phosphorus in relatively large amounts. When hydrolyzed, they sep- 

 arate into a proteid and a nuclein. 



The nucleins derived from cell nuclei can be still further separated 

 into a simpler proteid and nucleic acid, which latter in turn yields 

 phosphoric acid and the so-called purin bases, xanthin, hypoxanthin, 

 aaenin, and guanin. All nucleins which yield the purin bases are 

 termed true nucleins. 



The nucleins derived from caseinogen, vitellin, and probably cell 

 protoplasm can be separated by chemic methods into a proteid and 

 phosphoric acid only. For the reason that they do not give origin to 

 purin bases they are termed pseudo- or paranucleins. 



(a} Caseinogen. This is the principal proteid of milk, in which 

 it exists in association with an alkali, and hence was formerly 

 regarded as an alkali-albumin. It is precipitated by acetic 

 acid and by magnesium sulphate. It is coagulated by rennet 

 that is, separated into an insoluble proteid, casein or tyrein, 

 and a soluble albumin. Calcium phosphate seems to be the 

 natural alkali necessary to this process, for if it be removed 

 by dialysis, or precipitated by the addition of potassium oxalate, 

 coagulation does not take place. 



(b) Vitellin. Vitellin is a constituent of the vitellis or yolk of 

 eggs. It differs from other proteids in the fact that it is 

 semicrystalline in character. Though usually regarded as a 

 nucleo-proteid it is not definitely known whether or not it 

 contains phosphorus in its composition. 



