CONSTITUENTS OF THE HUMAN BODY. 19 



often of exactly similar composition, although very different in 

 their characters. One essential distinction is in regard to the 

 existence of nitrogen, upon which generally depends the rapidity 

 with which they pass into a state of decomposition (become 

 putrid). 



We therefore distinguish : 



6. 1. Nitrogenized Substances. 



1. Protein (discovered by Mulder), [C 40 H 31 N 5 0, 2 ], in the moist state 

 gelatinous; dried, brittle, and brownish; is scentless and tasteless, insoluble in 

 water, spirit and ether; soluble in all dilute acids, and forms with a little Sul- 

 phur and Phosphorus the following (albuminous) bodies. 



a. Albumen; [Pr 10 -f-P S 2 ], the most diffused of them, is, when dried, yel- 

 lowish, brittle, soluble in cold water, coagulable by heat, creosote, spirits of 

 wine, and unites insolubly with nitric and tannic acid, Plumb, diacet, alum, 

 Corrosive sublimate, &c. It is found in Lymph, Chyle, Serum of blood, and 

 especially in the Brain. 



b. Fibrin; [Pr, -f- P S], readily coagulates (within 3 7 minutes), is fibrous, 

 reteform; is present in a soluble condition in the blood, from which it is ob- 

 tained by whisking it with twigs, coagulated in the muscles. Vegetable acids 

 (and their salts) and caustic alkalies hinder the coagulation. Coagulated fibrin 

 decomposes super-oxyde [Binoxyde] of Hydrogen in water, not albumen ; the 

 latter becomes violet with Hydrochloric acid, the former indigo blue. 



c. Casein; [Pr 10 -\- S], soluble in water, pale yellow in solution, coagulates 

 (membranous upon milk) by boiling (in flakes), by Alcohol, Acids (particu- 

 larly lactic), and rennet. It is found in milk, blood, saliva, bile, and pancreatic 

 fluid, lens. 



d. Pepsin; (discovered by Schwann) [C 48 H 32 N 8 10 Vogel], in the gastric 

 juice, in the parietes of the gastric glands, and upon other mucous membranes; 

 precipitates by acetate of lead, dissolves with some acid, albumen and fibrin, 

 very readily (digestion) ; is very like albumen ; loses by coagulating the soluble 

 property; also by bile. 



e. Globulin; [Prj 5 -f- S], that is, the envelopes and nuclei of the (microscopic) 

 blood corpuscles, without the coloring matter, insoluble in Alcohol ; very like 

 albumen. Is (according to Fr. Simon) Casein united with Hsematin. 



f. Spermatin; in the seminal fluid, is probably only fibrin ; is soluble in water, 

 becoming a clear fluid, which does not coagulate by boiling. 



g. Mucus; consists of the secretion of the mucous glands, the cast-off epithe- 

 lium of mucous membranes, and usually also of pus ; swells up in water, is 

 soluble in strong acids, and precipitated by tannin. 



h. Peculiar matter of tears; dries in the air to a yellow, insoluble mucus; in 

 acids and heat not coagulable. 



i. Keratin; [Pr S 2 ], the seemingly homogeneous matter of Epithelium, Hair, 

 Nails, consists of different substances, like e, f, g, the chemical relations of which 

 are not yet singly determined. 



[NOTE. There are great doubts as to the existence of " Protein."] 



2. Extractive Matters. 



7. Not less difiused than the Protein compounds, is the animal extractive 

 matter, which is particularly obtained from muscular substance (flesh), by 



