24 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



Filter off the precipitate and test the filtrate for protein. 

 Compare this reaction with the similar one for albumin. 



(e) Cool 10 c.c. of the globulin solution to about C. 

 and let C0 2 gas bubble through it. Note result. 



(/) Take 10 c.c. of blood-serum and saturate it with 

 MgS0 4 . What is this precipitate? Filter, and to the fil- 

 trate add two drops of acetic acid. What is this second 

 precipitate? Test both precipitates for protein. 



ALBUMINOIDS. 



The albuminoids form a class of substances of hetero- 

 geneous nature closely allied to the proteins, but exhibiting 

 also marked differences. They form the chemical basis of 

 the skeletal and epidermal structures and the variations in 

 the properties, and characteristics which are observed in 

 them are probably dependent upon morphological changes. 

 In general they occur in an insoluble form and are charac- 

 terized by their resistance to reagents which tend to dissolve 



them. 



COLLAGEN. 



Collagen occurs as the chief constituent of connective 

 tissue (e.g., cartilage) and also as the organic matrix of bone 

 (ossein). It is easily hydrated by boiling with water or 

 weak acids and is then converted into gelatin, which on 

 this account may be considered as the hydrate of collagen. 



GELATIN. 



Gelatin possesses the characteristic of forming, with hot 

 water, solutions which set in a jelly upon cooling, if the con- 

 centration is greater than 1 per cent. 



Finely cut tendons or bones from which the salts have 



