12 HUMAN PHYSIOLOGY 



proteoses, which are precipitated in a saturated solution of 

 common salt, NaCl. 



(6) Those more nearly allied to the peptones Deutero- 

 proteoses, which are not precipitated in a saturated solution 

 of NaCl, but are precipitated by a saturated solution of 

 sulphate of ammonia. 



3. Peptones. These are the ultimate products of the 

 action of gastric juice on proteids. Their characteristic 

 reaction is their solubility in hot saturated sulphate of 

 ammonium solution. They diffuse very readily through 

 an animal membrane. 



(B) Conjugated Proteids. Proteids have a great tendency 

 to link with other substances 



(1) Proteates are formed by linking acids or alkalies to the 

 native proteids. 



(2) Nucleins, so called because their existence was first 

 demonstrated in the nuclei or central parts of the cells of 

 the body, may readily be split into a proteid part and 

 into nucleic acid, a phosphorus - containing material of 

 definite composition, having an acid reaction, and containing 

 about 10 per cent, of phosphorus. In certain places the 

 amount of nucleic acid is large in proportion to the proteid, 

 in others it is small. The term nuclein is usually confined 

 to the former, nucleo-albumin to the latter of these. From 

 the pure nucleic acid, which occurs along with protamine 

 in the heads of spermatozoa, to the proteids almost free of 

 phosphorus there is a continuous series. 



Nucleic acid when decomposed yields phosphoric acid and 

 a series of bodies called the Purin bodies which belong to the 

 class of diureides, and consist of two more or less modified 

 urea molecules linked together by the radicle usually of 

 acrylic acid (see p. 397). 



(3) Pseudo-Nucleins. Other compounds of proteids with 

 phosphorus-containing molecules occur which do not yield 

 purin bodies when decomposed. Of these vitellin, the pro- 

 teid of the yolk of egg, is an example. 



(4) Histones are proteids linked to protamine. They occur 

 in the globin which may be separated from blood pigment. 

 They have a basic reaction. 



(5) Glyco-proteids. Proteids are linked with sugar-like 



