32 PHYSIOLOGY. 



bases, lysin, histidin, and arginin. Protamin has been found loosely 

 combined with nucleic acid in the spermatozoa of fishes. In the pro- 

 teid molecule it is firmly combined with the amido acids, like leucin, 

 glycin, and usually with the aromatic bodies, like tyrosin, etc., and 

 inorganic elements, like sulphur and phosphorus. 1 



The proteids of different animals seem, to rough chemical tests., 

 to be the same; but the precipitin test shows a difference between 

 them. The casein of cow's milk is not exactly similar to that of' 

 woman's milk. 



More is required than a mere equivalent of nitrogen to cover 

 the loss of nitrogen from the body. 



Polypeptids. 



In the first ten years of the nineteenth century Chevreul laid 

 bare the nature of fats in the process of the making of soaps, and 

 in 1854 Berthelot, by means of glycerin and fat acids, constructed 

 synthetically a fat. In 1890 grape sugar was synthetically produced 

 by Fischer. As regards proteins, Miescher, in 1874, detected in the 

 semen of the salmon the protamins. In the last few years Fischer 

 has been able to unite the amido-acids. He has made a body 

 containing 14 amido-acids. It is called l-leucin-triglycyl-l.-leucyl- 

 oktaglycyl-glycin. Organic synthesis is not yet eighty years old, 

 for Woehler first produced urea in 1828. Fischer hopes shortly to 

 produce peptones from the polypeptids. 



Proteids consist of long chains of relatively simple molecules, 

 which by hydrolysis into ammo-acids are the keystones of the 

 proteid compound. 



When proteids are split up by either ferments or chemical 

 agents, the general order of the products is the same. The first 

 action is to produce proteids which have smaller molecules than the 

 original native albumin. These products are denominated albu- 

 moses. The next stage is the formation of still smaller molecules of 

 peptone, and finally the peptone breaks up into smaller crystalline 

 materials of known composition, which do not give typical proteid 

 reactions. The above chemical reactions are hydrolyses. 



These bodies can be arranged into groups: 



(1) Monoamino acids, such as glycin or glycocoll, leucin, aspar- 

 tic acid, glutaminic acid, etc. 



(2) Diamino acids, as lysin, arginin, valeric acid, containing a 



^eddard, "Practical Physiology." 



