ORGANIC SUBSTANCES. 97 



with alkalies, they do not play the part of an acid towards the base, 

 or of a base towards the acid ; for the acid or alkaline reaction of 

 the substance employed is not neutralized, but remains as strong 

 after the combination as before. Futhermore, the union does not 

 take place, so far as can be ascertained, in any definite proportions. 

 The organic substances have, in fact, no combining equivalent ; and 

 their molecular reactions and the changes which they undergo in 

 the body cannot therefore be expressed by the ordinary chemical 

 phrases which are adapted to inorganic substances. Their true 

 characters, as proximate principles, are accordingly to be sought 

 for in other properties than those which depend upon their exact 

 ultimate composition. 



One of these characters is that they are hygroscopic. As met with 

 in different parts of the body, they present different degrees of con- 

 sistency ; some being nearly solid, others more or less fluid. But on 

 being subjected to evaporation they all lose water, and are reduced 

 to a perfectly solid form. If after this desiccation they be exposed 

 to the contact of moisture, they again absorb water, swell, and 

 regain their original mass and consistency. This phenomenon is 

 quite different from that of capillary attraction, by which some in- 

 organic substances become moistened when exposed to the contact 

 of water ; for in the latter case the water is simply entangled me- 

 chanically in the meshes and pores of the inorganic body, while that 

 which is absorbed by the organic matter is actually united with its 

 substance, and diffused equally throughout its entire mass. Every 

 organic matter is naturally united in this way with a certain quantity 

 of water, some more and some less. Thus the albumen of the blood 

 is in union with so much water that it has the fluid form, while the 

 organic substance of cartilage contains less and is of a firmer con- 

 sistency. The quantity of water contained in each organic sub- 

 stance may be diminished by artificial desiccation, or by a deficient 

 supply ; but neither of them can be made to take up more than a 

 certain amount. Thus if the albumen of the blood and the organic 

 substance of cartilage be both reduced by evaporation to a similar 

 degree of dryness and then placed in water, the albumen will absorb 

 so much as again to become fluid, but the cartilaginous substance 

 only so much as to regain its usual nearly solid consistency. Even 

 where the organic substance, therefore, as in the case of albumen, 

 becomes fluid under these circumstances, it is not exactly a solution 

 of it in water, but only a reabsorption by it of that quantity of fluid 

 with which it is naturally associated. 

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