14 TEXT-BOOK OF PHYSIOLOGY 



to undergo disintegration and reduction to simpler compounds. This 

 decomposition or putrefaction occurs most readily when the conditions 

 most favorable to the growth of bacteria are present viz., a temperature 

 varying from 25C. to 4oC., moisture, and oxygen. The intermediate 

 as well as the terminal products of the decomposition of the proteins are 

 numerous, and vary with the composition of the protein and the specific 

 physiologic action of the bacteria. Among the intermediate products 

 is a series of alkaloid bodies, some of which possess marked toxic 

 properties, known as ptomains. The toxic symptoms which frequently 

 follow the ingestion of foods in various stages of putrefaction are to 

 be attributed to these compounds. The terminal products are repre- 

 sented by hydrogen sulphid, ammonia, carbon dioxid, fats, phosphates, 

 nitrates, etc. 



Classification. The animal proteins by virtue of their structural 

 composition, their physical and chemic properties, permit of a provisional 

 arrangement into three groups as follows: Simple proteins, conjugate 

 proteins and protein derivatives. 



SIMPLE PROTEINS 



The simple proteins are so called because of the fact that when they 

 are hydrolyzed they yield only a-amino- and diamino-acids. The members 

 of this group are as follows: 



PROTAMINS. 



These proteins are derived for the most part from the heads of the sper- 

 matozoa of fish. They take their names from the species of fish from 

 which they are obtained, e.g., salmin (salmon), sturin (sturgeon), scom- 

 brin (mackerel), etc. Inasmuch as they respond to Piotrowski's test in a 

 characteristic way they are regarded as true proteins.. When subjected to 

 hydrolysis they can be resolved into the diamino bodies, lysin, arginin and 

 histidin, of which they constitute about 90 per cent., and a small number of 

 the mono-amino-acids. Because of the fact that the diamino bodies, lysin, 

 histidin and arginin contain 6 atoms of carbon they are known as the hexone 

 bases. Inasmuch as the protamins contain practically but these three 

 bodies, they are regarded as the simplest of all the proteins. Since a typical 

 protein always yields on hydrolysis the hexone bases, in addition to a variable 

 number of mono-amino-acids, it is believed that the usual protein is com- 

 posed of a nucleus of the hexone bases to which is attached a variable 

 number of mono-amino-acids. The proportions in which the bases exist 

 in the nucleus and the proportions in which the amino-acids are united to 

 the nucleus, vary in different proteins. 



HISTONS. 



The proteins embraced in this class comprise a series of compounds 

 which are somewhat more complex than the protamins and less complex 

 than the typical proteins; for on hydrolysis they not only yield the hexone 

 bases but in addition a large number of mono-amino-acids. They are, there- 

 fore, intermediate in structural composition between the protamins and the 

 usual proteins. Their protein character is indicated by their reaction to 

 Millon's reagent and to Piotrowski's test. They are precipitated from 



