ELEMENTS OF COMPOSITION. 17 



peculiar reactions, as well as in almost all cases for the property of coagu- 

 lating at comparatively low temperatures, ranging from 35 to 50 C. 



One of these substances, the myosin of Kuhne, coagulates after death, 

 and is thus the cause of rigor mortis. Coagulated myosin is not soluble in 

 pure water, but is readily so in such containing as little as ten per cent, of 

 chloride of sodium. It may likewise be dissolved in dilute acids and 

 alkalies. It has the same action upon superoxide of hydrogen as fibrin. 



Beside myosin, the fluids with which muscle is saturated contain three 

 other soluble albuminous matters, namely, an albuminate of potash, and 

 two substances which coagulate, one at 45 C., and another at 75 C. 



From dead muscle, but also from other albuminous materials, a muta- 

 tion product has been extracted by very dilute acids, to which the name 

 of mmde fibrin or syntonin has been given by Lehmann. In contradis- 

 tinction to the fibrin of blood, it is soluble in water containing 0*1 per cent, 

 of hydrochloric acid, but not so in solutions of nitrate and carbonate of 

 potash. It has no effect, moreover, upon superoxide of hydrogen. 



Casein. 



This protein substance, which is probably an albuminate of potash, does 

 not pass from the soluble to the insoluble form spontaneously, like fibrin, 

 but on coming into contact with the mucous membrane of the stomach. 

 On being heated, liquids in which it is contained become covered with a 

 thin pellicle, consisting of casein modified by the oxygen of the air. 

 Casein is precipitated by acids in flakes, and in contradistinction to 

 albumen by acetic acid. According to Lehmann it is not thrown down 

 from milk by a stream of carbonic acid. 



This substance forms the chief constituent of the milk of man and the 

 mammalia, and the most important aliment for the infant. How far it is 

 besides distributed through the system is still uncertain ; its presence in 

 alkaline fluids, however, is very probable. It is said to exist in the 

 middle coats of arteries by M. Schultze. 



Globulin. Crystallin. 



By these names are known certain albuminous substances coagulating 

 like albumen when heated. They require, however, a higher temperature, 

 and then separate either in the form of a globular mass or milky coagulum. 

 A solution of globulin, acidulated with acetic acid, is said to be pre- 

 cipitated by careful neutralisation with ammonia, and an ammoniacal 

 solution by acetic acid. Globulin is entirely thrown down in fluids by a 

 stream of carbonic acid. 



Many things have in course of time received the name of globulin. 



It is found in the lens, in blood-cells (?), in the plasma of the blood, as 

 fibrinogen and fibrinoplastin ( 11), and in exudations. 



Peptones. 



The albuminoids entering into the composition of tissues, as we have 

 just seen, do not possess the power, when in watery solution, of passing 

 through animal membranes. They are colloids in Graham's sense of the 

 word (p. 14). 



These, on being received into the body, partly from the animal and 

 partly from the vegetable kingdom, are all converted by the processes of 



