CHEMICAL COMPOSITION OF THE TEXTURES. v 



occur in the living body, and seems indeed to be indispensable for the main- 

 tenance and manifestation of life. 



All the soft tissues contain water, some of them more than four-fifths of their 

 weight ; this they lose by drying, and with it their softness and flexibility, and so 

 shrink up into smaller bulk and become hard, brittle, and transparent ; but when the 

 dried tissue is placed in contact with water, it greedily imbibes the fluid again, and 

 recovers its former size, weight, and mechanical properties. The imbibed water is no 

 doubt partly contained mechanically in the interstices of the tissue, and retained 

 there by capillary attraction, like water in moist sandstone or other inorganic porous 

 substances ; but the essential part of the process of imbibition by an animal tissue is 

 not to be ascribed to mere porosity, for the fluid is not merely lodged between the 

 fibres or laminae, or in the cavities of the texture; a part, probably the chief part, is 

 incorporated with the matter which forms the tissue, 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 substance. Be this as it may, it is clear that the tissues, even in 

 their inmost substance, are permeable to fluids, and this property is indeed necessary, 

 not only to maintain their due softness, pliancy, elasticity, and other mechanical 

 qualities, but also to allow 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 being resolved by 

 ultimate analysis into chemical elements, or simple constituents, not differ- 

 ing 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 body, though it must be remarked, that some of 

 them occur only in exceedingly minute quantity, if indeed they be constant : 

 oxygen, hydrogen, carbon, nitrogen, phosphorus, sulphur, chlorine, fluorine, 

 potassium, 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 constituents 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 consti- 

 tuents 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 

 albumen, fibrin, and fat, are peculiar to organic bodies, and are accordingly 

 named the proximate organic principles. 



The animal proximate principles have the following leading characters. 

 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, phosphuretted, and carburetted hydrogen gases. 

 The immediate compounds found in the solids and fluids of the human body 

 are the following. 



I. Azotised Substances, or such as contain nitrogen, viz., albumen, blood- 

 fibrin, muscle-fibrin (or syntonin), casein, globulin, gelatin, chondrin, extrac- 

 tive soluble in alcohol, extractive soluble in water, salivin, kreatin, kreatinin, 

 pepsin, mucus, horny matter or keratin, pigment, hsematin, pyin, urea, uric 



