14 TEXT-BOOK OF PHYSIOLOGY 



liquid to the solid state. The colloid character of the proteins permits 

 of their separation and purification from crystalloid diffusible com- 

 pounds by the process of dialysis. 



2 . Solubility. Some of the proteins are soluble in water, others in solutions 



of the neutral salts of varying degrees of concentration, in strong acids 

 and alkalies. All are insoluble in alcohol and ether. 



3. Coagulability. Under the influence of heat and animal ferments, 



some of the proteins readily pass from the soluble liquid state to the 

 insoluble solid state, attended by a permanent alteration in their chemic 

 composition. To this change the term coagulation has been given. 

 The various proteins, however, coagulate at different temperatures. 

 Proteins are capable of precipitation without losing their solubility 

 by ammonium sulphate, sodium chlorid, and magnesium sulphate. 



4. Fermentability. In the presence of specific microorganisms bacteria 



the proteins, owing to their complexity and instability, are prone 

 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 



