1170 PROTEIDS. 



coagulated by heat; (2) that when the solution is carefully 

 neutralized the whole of the proteid is thrown down as a pre- 

 cipitate ; in other words, the serum-albumin, which was soluble 

 in water, or at least in a neutral fluid containing only a small 

 quantity of neutral salts, has become converted into a substance 

 insoluble in water or in similar neutral fluids. The body into 

 which serum-albumin thus becomes converted by the action of 

 an acid is spoken of as acid-albumin. Its characteristic features 

 are that it is insoluble in distilled water, and in neutral saline 

 solutions, such as those of sodic chloride, that it is readily 

 soluble in dilute acids or dilute alkalis, and that its solutions 

 in acids or alkalis are not coagulated by boiling. When sus- 

 pended, in the undissolved state, in water, and heated to 75° C, 

 it becomes coagulated, and is then undistinguishable from 

 coagulated serum-albumin, or indeed from any other form of 

 coagulated proteid. 



Globulins are more readily converted into acid-albumin than 

 are the native albumins. Coagulated proteids or fibrin require 

 for their conversion the application of the acids, preferably 

 hydrochloric, in a concentrated form, the products thus obtained 

 being practically undistinguishable from the products of the 

 action of dilute acids on the more readily convertible proteids. 



2. Syntonin. 



Although this substance is merely the acid-albumin which 

 results from the action of acids on the globulin (myosin) con- 

 tained in muscles, and in its more obvious properties is at first 

 sight identical with other acid-albumins, it merits a short 

 and separate description, not only on account of its historical 

 interest in the chemistry of muscles but also because recent 

 work has shewn it to be distinctly different from the similar 

 products of the action of acids on other proteids, and its prop- 

 erties and reactions have been more fully studied than those of 

 any other form of acid-albumin. 



The reactions specially characteristic of this substance and 

 its distinctions from other forms of acid-albumin and from 

 alkali-albumin are indicated in the following statements. 



1. It is soluble in lime-water, and this solution is coagu- 

 lated, though incompletely, by boiling. 



2. It is insoluble in acid phosphate of soda (NaH 2 P0 4 ), 

 other acid-albumins are soluble. In presence of this salt it 

 does not pass into solution on the addition of alkali until the 

 whole 'of the acid phosphate has been converted into the neutral 

 (Na 2 HP0 4 ). In this respect it differs from alkali-albumin, 

 which is soluble under the same conditions long before the 

 conversion of the acid into the neutral phosphate is complete. 



3. It is soluble in dilute sodium carbonate. 



