82 CHEMICAL COMPOSITION OF THE BODY. 



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and the following table 1 will show the close similarity in the composition of 

 those that have been most carefully determined. They are all very unsta- 



Serum-albumen. Fibrin. Syutonin. Globulin. Casein. 



ble, and riot only easily decompose themselves, but act as excitors of fermen- 

 tation to other bodies. Most of the Proteids exist in two states a soluble, 

 and an insoluble. The former may be obtained by evaporating the fluids in 

 which they are contained at a comparatively low temperature to dryness, 

 when the albuminous substance appears as a semi-transparent yellowish 

 material, resembling gum-arabic, free from taste and smell, neutral to test- 

 paper, and with the exception of Haemoglobin, quite destitute of any ten- 

 dency to crystallize. The insoluble form is obtained by heat or by precipi- 

 tation with various chemical reagents, and forms whitish flocculeut masses, 

 which present a granular aspect under the microscope. A moderately strong 

 solution of ov-albumen in water becomes turbid at 140 ; completely insolu- 

 ble at 145 ; and separates in flakes at 167 ; when excessively diluted, 

 however, no turbidity can be produced by a less heat than 194 . After 

 having been dried in vacuo, or at a temperature below 120, albumen may 

 be heated to 212 without passing into an insoluble condition. The albu- 

 minous compounds belong to the group of Colloids, founded by Professor 

 Graham, which possess an extremely low power of diffusion through animal 

 membranes. To this peculiarity their feeble taste may in all probability be 

 attributed. They have little or no smell. They dissolve in concentrated 

 acetic arid phosphoric acids, and with partial decomposition in caustic 

 alkalies. They are precipitated by alcohol, ether, taunic acid, corrosive 

 sublimate, and most of the mineral acids. Concentrated nitric acid stains 

 them yellow, and concentrated hydrochloric acid dissolves them, the solu- 

 tion assuming a blue color. They are precipitated by potassium ferrocyauide. 

 Solution of iodine stains them of a yellow color, and they all become red at 

 212 F. when acted on by Millon's reagent, which consists of a solution of 

 the proto- and pernitrate of mercury. Sulphuric acid holding molybdenic 

 acid in solution stains them of a dark blue (Frohde's reaction), and when 

 treated with sugar and sulphuric acid under the microscope, they give a 

 beautiful violet color (Schultze's reaction). You Gorup Besanez 2 observes 

 that when acted on by powerful oxidizing agents, the albuminous compounds 

 yield formic, acetic, propiouic, butyric, valerianic, capronic, and benzoic 

 acids, the aldehydes of these acids, ammonia, and volatile bases ; whilst by 

 the action of acids, alkalies, and during putrefaction, they give rise to vola- 

 tile fatty acids, leucin, tyrosin, glycin, ammonia, volatile bases, sulphide of 

 ammonium, and a volatile crystallizable substance having the odor officers. 

 It is worthy of notice that some of these, as the azotized compounds, leuciu, 

 and tyrosin, and the uonazotized substance, glycin, can be extracted from 

 those parts of the body as the glands in which active processes of metamor- 

 phosis are taking place. It is reasonable to suppose, therefore, that the suc- 

 cessive stages undergone by the albuminous substances within the body are 

 essentially similar to those through which they pass when acted on by 

 chemical agents without the body. The aqueous solutions of albumen rotate 

 the plane of polarization to the left. 



1 Frey, Histoelieinic, 1873, p. 13. 2 Phys. Chemii>, 1874, pp. 39 and 117. 



