84 THE CHEMICAL COMPOSITION OF THE BODY 



water unto all the blood-coloring matter is removed. It is soluble to a cer- 

 tain extent in strong sodium-chloride solutions. 



Proteoses. These are intermediate substances of the digestion 

 of other proteids, the ultimate product of which is peptone or lower cleavage 

 products. They are produced by the action of the gastric and pancreatic 

 juices and also, slowly, by boiling with dilute acids. The term is a general 

 one, the proteose of albumin being albumose, that of globulin being globu- 

 lose, etc. They are divided into primary and secondary groups representing 

 the stages of progression from proteids to peptones, so that there may be a 

 primary and a secondary albumose, etc. As digestion is a process of hydra- 

 tion with cleavage, the successive stages present progressively simpler sub- 

 stances. Each group reacts to fewer reagents than the preceding one; e.g., 

 none of the proteoses can be coagulated by boiling. Nitric acid will precipi- 

 tate the primary proteoses but not the secondary ones. 



Peptones. Peptone is formed by the action of the digestive fer- 

 ments, pepsin or trypsin, on other proteids, and on gelatin. It is a still 

 simpler form of substance than the proteoses and reacts to still fewer reagents. 

 Peptones will be considered in connection with the physiology of digestion, 

 as will also be the intermediate compounds. 



Histons. Histons are decomposition products but present well- 

 defined proteid reactions. They are strongly basic and have a large con- 

 tent of hexon bases. Histons are soluble in water; are precipitated by weak 

 ammonia; are soluble in acids; do not coagulate by heat in water solutions 

 unless salts are present. They are not changed by and may be recovered 

 from the salt heat coagulation. They do not contain phosphorus. They 

 give the biuret reaction, but do not give Millon's reaction. 



Protamin. This substance is of special interest in that it is the 

 simplest of the proteids. It is a cleavage product which exists in nature in 

 fish sperm as a nucleic acid compound. It gives the biuret but not Millon's 

 reaction, is not coagulated by heat. It yields amido-acids as cleavage-prod- 

 ucts. These cleavage-products have been recently resynthesized by Taylor 

 by the action of trypsin. 



Compound Proteids. The compound proteids are compounds 

 of a simple proteid with some other molecule. According to their chemical 

 composition and characteristics they are divided into several classes, viz.: 

 Chromo proteids. This is a combination of a proteid substance with some 

 form of pigment. For example, hemoglobin is a combination of a globulin 

 with hematin, an iron-containing radicle. Hemoglobin is described more 

 fully in the chapter on the Blood. Nucleo proteids. Nucleoproteids are a 

 combination of a proteid substance with a nucleic acid; they are divided 

 into two groups according to the character of the acid. The true nucleo- 

 proteids contain true nucleic acid; the para-nucleoproteids or pseudo-nucleo- 

 proteids contain para-nucleic acid. Both acids, and therefore both groups, 



