70 MANUAL OF PHYSIOLOGY. 



C. Derived Albumins (Albuminates). 



1. Acid Albumin (Syntonin) can be made from any of the pre- 

 ceding by the slow action of a weak acid ; or by the addition of 

 strong acetic or hydrochloric acids to native albumin, such as 

 exists in white of egg, and dissolving the jelly, thus formed, in 

 water. It is only soluble in weak acids exact neutralization 

 precipitating it. With the least excess of alkali the precipitate 

 redissolves, becoming changed into alkali albumin. 



So long as it is dissolved in weak acid it will not coagulate on 

 boiling, but it coagulates and becomes incapable of re-solution if 

 heated while precipitated by neutralization. 



2. Alkali Albumin. Similar to the last, but produced by the 

 action of either weak alkalies and dilute solutions, or strong 

 solution of potash on white of egg. Its general behavior is the 

 same as the above, but it differs in composition, containing no 

 sulphur if prepared with strong KHO and allowed to stand. It 

 can then be distinguished by the absence of the brown coloration 

 which appears on heating acid albumin with caustic potash and 

 lead acetate. 



3. Casein is the proteid existing in milk, and resembles alkali 

 albumin in its reactions. It can be precipitated from milk by 

 rennet, or acetic acid in excess, but not by exact neutralization, 

 owing to the presence of potassium phosphate. 



D. Fibrin. 



A solid filamentous body, the result of chemical changes ac- 

 companying the death of the blood plasma, during which the 

 so-called fibrin generators are set free. It swells in weak hydro- 

 chloric acid, but does not dissolve while cold. If heated to 60 C. 

 in acid, it changes to acid albumin and dissolves. By 10 per 

 cent, neutral saline solutions, a substance like a globulin may be 

 extracted from it. If heated, it assumes the characters of a 

 coagulated proteid. 



E. Coagulated Albumin. 



If any of the above be heated to 70 C. (except acid and alkali 

 albumin, which must first be precipitated by neutralization), they 



