THE PKOTEINS 



37 



as the tendency to coagulate or solidify and the readiness with 

 which they are ' salted out,' are shared in common with other colloids 

 some of which ai e of inorganic nature. 



All proteins are soluble with the aid of heat in concentrated 

 mineral acids and alkalis. Such treatment, however, decomposes as 

 well as dissolves the protein. Proteins are also soluble in gastric and 

 pancreatic juices ; but there, again, they undergo a change, being 

 converted by hydrolysis into proteins of smaller molecular 

 weight called peptones. The intermediate substances formed in this 

 process are called proteoses. Commercial peptone contains a mixture 

 of proteoses and true peptone. 



Heat Coagulation. Many of the proteins which are soluble in 

 water or saline solution are rendered insoluble when those solutions 



FIG. 7. Dialyser. The lower opening of the bell jar 

 suspended in water is tightly covered with parchment 

 paper. The fluid to be dialysed is placed within this 

 vessel ; the crystalloids pass out into the distilled 

 water outside through the parchment paper. 



FIG, 8. In this form of dialyser 

 the substance to be dialysed 

 is placed within the piece 

 of tubing suspended in the 

 larger vessel of water. The 

 tubing is made of parchment 

 paper. 





are heated. This is true for most of the proteins that occur in nature. 

 The solidifying of white of egg when heated is a familiar instance of 

 this. The temperature of heat coagulation differs in different pro- 

 teins : thus myosinogen and fibrinogen coagulate at about 56 C. ; 

 serum albumin and serum globulin at about 75 C. 



The proteins which are coagulated by heating their solution come 

 for the most part into two classes the albumins and the globulins. 

 The full distinction between these we shall see immediately. We 

 may, however, state here that the albumins are soluble in distilled 



