CHEMICAL BASIS OF THE ANIMAL BODY. 875 



A peculiar property of this body remains yet to be mentioned, viz., its power of decomposing 

 hydrogen dioxide. Pieces of fibrin placed in this fluid, though themselves undergoing no change, 

 soon become covered with bubbles of oxygen ; and guaiacum is turned blue by fibrin in presence 

 of hydrogen dioxide or ozonized turpentine. 



Preparation. By vigorously stirring blood with a bundle of twigs and then 

 washing with water until it is quite white. If required perfectly pure and colorless 

 it should be prepared from plasma free from corpuscles. If the blood, before stir- 

 ring, be diluted with an equal bulk of water, the subsequent washing of the fibrin 

 is much facilitated, and it may readily be obtained quite white. Any adherent fats 

 may be removed by ether. 



When globulin, myosin, and fibrin are compared each with the other, it will be 

 seen that they form a series in which myosin is intermediate between globulin and 

 fibrin. Globulin is excessively soluble in even the most dilute acids and alkalies ; 

 fibrin is almost insoluble in these ; while myosin, though more soluble than fibrin, 

 is less soluble than globulin. Globulin again dissolves with the greatest ease in a 

 very dilute solution of 'sodic chloride. Myosin, on the other hand, dissolves with 

 difficulty ; it is much more soluble in a 10 per cent, than in a 1 per cent, solution 

 of sodic chloride ; and even in a 1 per cent, solution the myosin can hardly be said 

 to be dissolved, so viscid is the resulting fluid and with such difficulty does it filter. 

 Fibrin again dissolves with great difficulty and very slowly in even a 10 per cent, 

 solution of sodic chloride, and in a 1 per cent, solution it is practically insoluble. 

 When it is remembered that fibrin and myosin are, both of them, the results of 

 coagulation, their similarity is intelligible. Myosin is, in fact, a somewhat more 

 soluble form of fibrin, deposited not in threads or filaments but in clumps and 

 masses. 



CLASS V. Coagulated Proteids. 



These are insoluble in water, dilute acids and alkalies, and neutral saline solu- 

 tions of all strengths. In fact, they are really soluble only in strong acids and strong 

 alkalies, though prolonged action of even dilute acids and alkalies will effect some 

 solution, especially at high temperatures. During solution in strong acids and 

 alkalies a destructive decomposition takes place, but some amount of acid- or alkali- 

 albumin is always produced. 



Very little is known of the chemical characteristics of this class. They are pro- 

 duced by heating to 70 C. solutions of egg- or serum-albumin, globulins, suspended 

 in water or dissolved in saline solutions; by boiling for a short time fibrin suspended 

 in water or dissolved in saline solutions, or precipitated acid- and alkali-albumin sus- 

 pended in water. They are readily converted at the temperature of the body into 

 peptones by the action of gastric juice in an acid, or of pancreatic juice in an alka- 

 line medium. 



All proteids in solutions are precipitated by an excess of strong alcohol. If the 

 precipitant be rapidly removed they are again soluble in water, but if the precip- 

 itated proteids are subjected for some time to the action of the alcohol they are, 

 with the exception of peptones, coagulated and lose their solubility. It appears, 

 however, that the proteids contained in the aleurone-grains of plants are exceed- 

 ingly resistant to this coagulating action of alcohol. 1 



It seems scarcely necessary to point out the distinction in the use of the word " coagulation " 

 as applied to blood- or muscle- plasma on the one hand and to the action of heat and alcohol upon 

 proteids on the other. The difference is obvious when it is remembered that in the first case the 

 coagulation leads to the formation of fibrin (Class iv.),or myosin (Class in.), and that these bodies 

 may then further be coagulated by heat or alcohol as described above. 



CLASS VI. Peptones.' 2 ' 



Very soluble in water, and not precipitated from their aqueous solutions by the 

 addition of acids or alkalies, or by boiling. Insoluble in alcohol, they are precip- 

 itated with difficulty by this reagent, and are unchanged m the process ; they differ 

 from all other proteids in not being coagulated by prolonged exposure to alcohol. 

 They are not precipitated by cupric sulphate, ferric chloride, or, except in the in- 

 stances to be mentioned presently, by potassic ferrocyanide, and acetic acid. In 

 these points they differ from most other proteids. On the other hand, precipita- 



i See Vines, Journ. of Phvsiol., vol. iii. p. 108. 



[ 2 The albumoses are so closely related to peptones that they are commonly considered together 

 with peptones as a class.] 



