62 MANUAL OF PHYSIOLOGY. 



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 

 re-dissolves, becoming changed into alkali-albumin. 



80 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 as it differs in composition, containing no sulphur 

 it can therefore 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 accom- 

 panying the death of the blood-plasma, during which the so-called 

 fibrin generators are set free. It swells in weak hydrochloric 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 

 coagulate and become extremely insoluble and lose their former 

 characters. They are but very slightly acted on by weak acids, 

 even when warmed. Strong acids dissolve them, but this solution 

 is associated with a destructive change. They are, however, 



