110 PROTEIDS. 



with caustic potash a product was obtained which he regarded 

 as the basis of all albuminous substances, and to which he gave 

 the name of " protein." Under this theory proteids are supposed to 

 be modifications of protein, but the theory is an obsolete one, and 

 Mulder's protein is nothing more than alkali-albumin. Alkali- 

 albumin is produced in the small intestine when the albumins and 

 globulins of the food are acted upon by the alkali of the pancreatic 

 juice. 



GLOBULINS. 



The members of this group are soluble in dilute saline solu- 

 tions, as, for instance, 1 per cent, sodium chlorid, insoluble in 

 water, concentrated solutions of sodium chlorid, magnesium sul- 

 phate, and ammonium sulphate, and are coagulated by heat. 



The following table gives the temperatures at which the im- 

 portant globulins coagulate : 



Globulins. Temperature. 



Serum-globulin 75 C. 



Fibrinogen 56 



Myosinogen 56 



Crystallin 73 



Serum-globulin (Paraglobulin). Fibrinoplastin is another 

 name for this proteid, given to it at a time when it was believed 

 that it was connected with the process by which fibrin was formed, 

 as in the coagulation of blood. It exists in human plasma to the 

 extent of about 3 per cent. It exists also in lymph and chyle. 



Fibrinogen. This globulin is associated with serum-globulin 

 in plasma, lymph, and chyle. It is a substance of great interest, 

 inasmuch as upon its presence the coagulability of blood depends, 

 a process in which the soluble fibrinogen becomes insoluble fibrin. 

 It is precipitated by half-saturating with sodium chlorid, and by 

 this means may be separated from serum-globulin. 



Fibrin. Fibrin is obtained by whipping blood with twigs or 

 wires. The material that clings to these is fibrin together with 

 some of the blood-corpuscles, which become entangled in its 

 meshes. These may be washed out in running water. When ex- 

 amined with the microscope fibrin is seen to be made up of threads 

 which intertwine with one another, forming a network. Dry fibrin 

 is obtainable from blood to the amount of from 0.2 to 0.4 per 

 cent, of its weight. Its percentage-composition is C, 52.68 ; H, 

 6.83; N, 16.91 ; S, 1.10; O, 22.48. It is soluble in 5 to 10 per 

 cent, solutions of sodium chlorid, sodium sulphate, magnesium 

 sulphate, and some other salts. It swells in hydrochloric acid 

 of 0.2 per cent, strength and becomes acid-albumin and proteoses. 

 If pepsin is also present, this change takes place more quickly, 

 the fibrin becoming converted into two globulins, one coagulating 

 at 56 C. and the other at 75 C., and then becoming acid-albu- 



