ELEMENTS OF COMPOSITION. 15 



Of the first there are many varieties ; but all these differences are probably 

 dependent upon the admixture of other matters, such as alkalies or acids. 



Soluble albumen is precipitated by alcohol, mineral acids, tannic acid, 

 and the salts of most metals. A larger or smaller quantity is also thrown 

 down by the passage through it of a stream of carbonic acid. 



It becomes converted. into the insoluble modification as already men- 

 tioned by boiling; further, by the action of most acids, without, however, 

 being always precipitated. The alkalies likewise transform albumen into 

 a very insoluble substance, but do not throw it down. 



Albumen is not present in the animal juices in a pure state, but com- 

 bined with a certain proportion of soda, saline water being the solvent. 

 Such albumen has a weakly alkaline reaction, coagulates more in gelatin- 

 ous masses than in flakes, and is, on the whole, more soluble than in the 

 pure condition. A larger proportion still of soda may modify the coagu- 

 lation of albumen by heat in many ways. 



Coagulated albumen partakes of the same nature as the remaining pro- 

 tein substances in the same state. 



Entering the body with the protein substances of the food, ^ appears 

 as a constituent of blood, chyle, and lymph, and also of the fluids saturat- 

 ing various organs. Combined with some peculiar substances, it appears 

 to form the medulla of nerves. To what extent it exists in the system 

 in the coagulated form is a question difficult to answer in the present state 

 of science. It can hardly be doubted, however, that it does so occur, and 

 the finely granular contents of many animal cells are probably entirely or 

 partially composed of it. 



"VVe are likewise at fault when asked to indicate the histogenic signi- 

 ficance of albumen more in detail. It can hardly be doubted, however, 

 that it is of very great importance, in that it is the first protein substance 

 from which many of the others in the organism take their origin. 



n. 



Fibrin, Fibrinogen, and Fibrinoplastin. 



Fibrin has always been described as a substance which does not coagu- 

 late at boiling point, but, as the saying is, spontaneously, a short time after 

 the animal fluids in which it is dissolved during life are poured out of 

 the body. 



It coagulates more rapidly at a moderately high than at a low tem- 

 perature. The oxygen of the atmosphere has probably no accelerating 

 effect upon the process, for in the interior of the body it is observed to 

 take place in fluids which have come to a state of rest in closed cavities. 

 The process may be retarded by the presence in the fluid of carbonic 

 acid, or the addition of various alkaline salts, such as Glauber salt, for 

 instance. 



Coagulated fibrin can never be obtained pure, however ; for, in the 

 act of congelation, the numerous cellular constituents of the fluids in 

 which it is contained become entangled in it. It offers, besides, many 

 varieties for our consideration. In water acidulated with hydrochloric 

 acid, it swells up, without, however, dissolving (Lielig) in contrast to 

 syntonin obtained from muscle tissue (see below). Coagulated fibrin 

 is dissolved in solutions of various alkaline salts for instance, in nitrate 

 and carbonate of potash, when the temperature is somewhat elevated 

 forming a substance similar to albumen. According to Thenard, further, 



