160 COLLOIDS IN BIOLOGY AND MEDICINE 



Fibrin. 



Fibrin is the substance of blood plasma, which coagulates shortly 

 after the blood has left the vessels. Upon the clotting of plasma, 

 which contains no blood corpuscles, no jelly is formed, but character- 

 istic fibrous masses. Formerly it was thought that uncoagulated 

 fibrin, called fibrinogen (see p. 299), was something quite different 

 from fibrin. As a result of the investigations of HEKMA it is possible 

 that fibrinogen is the hydrosol of alkali fibrin. If fibrin is dissolved 

 in extremely dilute alkali we obtain a fluid having all the properties 

 of fibrinogen. Normal coagulation outside the blood vessels as well 

 as the resulting product must be sharply differentiated from fibrin 

 coagulated by heat. Fibrin coagulated by heat ceases to show the 

 swelling phenomena it possessed before it was heated ; it has become 

 hydrophobe. When coagulated, fibrin is an irreversible gel. In 

 weak acid and alkalis it swells and gradually goes into solution 

 following, as it does so, the same laws as does gelatin (see p. 68, 

 et seq.). MARTIN H. FISCHER* has studied its swelling under the in- 

 fluence of acids, bases and salts, and utilized his results for his theory 

 of edema (see p. 223, et seq.) 



Muscle albumin or myosin, the coagulation of which at death 

 causes rigor mortis, belongs to the same group as fibrin. 



Nucleins. 



Basic substances have been prepared from cell nuclei; histone 

 from the leucocytes of the thymus, fish roes, etc., as well as pro- 

 tamine, so thoroughly studied by A. KOSSEL and usually obtained 

 from the spermatozoa of several different kinds of fish. They do 

 not exist as such in these organs but occur in combination with acid 

 nucleins as nucleo-proteins and nucleo-histones. 



Neutral solutions of histone yield a precipitate containing very 

 little salt with solutions of egg albumin, casein and serum globulin. 

 When we recall that casein and globulin are of decided acid reaction, 

 their union with basic histone is quite easily understood. A priori, 

 it is improbable that the precipitate should contain 1 part histone, 

 2 parts casein and globulin and 1 part egg albumin, as has been 

 claimed. It has been shown by U. FRIEDEMANN and H. FRIEDEN- 

 THAL* that according to the relative concentration in which solutions 

 of histone and albumin are mixed, the precipitate will vary in com- 

 position; that the addition of NaCl changes the precipitation limits 

 and that fresh solutions have different precipitation limits than 

 older ones. All these facts point with certainty to the fact that 

 nuclein is not a definite chemical combination, but that nucleins are 

 colloid compounds consisting of a negative and a positive colloid. 



