CHEMICAL COMPOSITIOX OF THE TEXTURES. 3 



forms the tissl^e. and is in a state of union with it. more intimate than could 

 well be ascribed to the mere inclusion of a fluid in the pores of another 

 £iibstance. Be this as it may. it is clear that the tissues, even in their inmost 

 substance, are permeable to fluids, and this i^roperty is indeed necessary, not only 

 to maintain their due softness, pliancy, elasticity, and other mechanical qualities, 

 Ijut also to alien- matters to be conveyed into and out of their substance in the 

 process of nutrition. 



CHEMICAL COMPOSITION. 



Ultimate Constituents. — The human body is capable of bcini^ 

 resolved by ultimate analysis into chemical elements, or simple consti- 

 tuents, not differing in nature from those which compose mineral 

 substances. Of the chemical elements known to exist in nature, the 

 following have been discovered in the human bod}', though it must be 

 remarked, that some of them occur only in exceedingly minute quan- 

 tity, if indeed they be constant : oxygen, hydrogen, carbon, nitrogen, 

 phosphorus, sulphur, chlorine, fluorine, ]:)otassium, sodium, calcium, 

 magnesium, iron, silicon, manganese, aluminium, copper. 



Proximate Constituents. — The ultimate elements do not directly 

 form the textures or fluids of the body ; they first combine to form 

 certain compounds, and these appear as the more immediate consti- 

 tuents of the animal substance ; at least the animal tissue or fluid 

 yields these compounds, and they in their turn are decomposed into the 

 ultimate elements. Of the immediate constituents some are found 

 also in the mineral kingdom, as for example, water, chloride of sodium 

 or common salt, and carbonate of lime ; others, such as albumin, fibrin, 

 and fat, are peculiar to organic bodies, and are accordingly named the 

 proximate organic principles. 



The animal proximate principles have the following leading cha- 

 racters. They all contain carbon, oxygen, and hydrogen, and the 

 greater number also nitrogen ; they are all decomposed by a red heat ; 

 and, excepting the fatty and acid principles, they are, for the most part, 

 extremely prone to putrefaction, or spontaneous decomposition, at least, 

 when in a moist state ; the chief products to which their putrefaction 

 gives rise being water, carbonic acid, ammonia, and sulphuretted, phos- 

 phuretted, and carburetted hydrogen gases. The immediate compounds 

 obtained from the solids and fluids of the human body are the following. 



I. Azofiscd Suhsfances, or such as contain nitrogen, viz., albumin, 

 blood-fibrin, myosin, syntonin, casein, globulin, gelatin, chondrin, 

 salivin, kreatin, kreatinin, pepsin, mucin, horny matter or keratin, pig- 

 ment, h[Emoglobiu, urea, uric acid, hippuric acid, inosinic acid, sarkin 

 (or hypoxanthiu), leucin, tyrosin, protagon and its components lecithin 

 and neurin, azotised biliary compounds. 



II. Substances desiituie of Niirogen, viz., fatty matters, glycogen (or 

 animal starch), grape sugar, sugar of milk, inosit, lactic, formic, and 

 oxalic acids, certain princi])les of the bile. 



Some of the substances now enumerated require no further notice in 

 Tj work devoted to anatomy. Of the rest, the greater numljer will be 

 explained, as far as may be necessary for our purpose, in treating of the 

 particular solids or fluids in which they are chiefly found. 



It has been shown by Graham,* that chemical substances may be distingnished 

 * Liquid Diffusion applied to Analysis, — Pliil, T]-ans., 1S61. 



