i 4 TEXT-BOOK OF PHYSIOLOGY. 



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 o the fact that when they 

 are hydrolyzed they yield only 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- 

 brom (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 heocone 

 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 certain number of 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. The histons are usually found 

 in combination with nucleic acid, in the spermatozoa of most animals and 

 especially in fish, and in the coloring matter (the hemoglobin) of the red 

 corpuscles. The proteins of the tissues usually contain from 25 to 30 per 

 cent, of histons. 



