NITROGENOUS HISTOGENETIC SUBSTANCES. 323 



genous products, namely the nitriles of some of the acids of the 

 butyric acid group. 



Some few of these substances are dissolved by the caustic 

 fixed alkalies in such a manner, that they can be again precipi- 

 tated by acids in a perfectly unchanged condition ; but the 

 majority can only be dissolved in a concentrated alkaline solution, 

 and with the continued application of heat, by means of which they 

 become perfectly decomposed. Since the greater number of the 

 bodies belonging to this group contain sulphur in addition to the 

 ordinary elements of organic substances, the first effect produced 

 by the action of heated dilute alkaline solutions is the abstraction 

 of the sulphur by the formation of liver of sulphur and of alkaline 

 hyposulphites. There is always a development of ammonia, 

 although this is most considerable when concentrated alkaline solu- 

 tions are used; carbonic and formic acids volatilise with the ammonia, 

 while new bodies appear in the decoction, having either an acid, 

 or a nitrogenous basic, or indifferent character, as for instance, 

 leucine, glycine, protide, &c. If these substances be mixed with 

 alkalies and gently fused, there will appear a large quantity of 

 cyanide of potassium, leucine, tyrosine, &c., besides the ordinary 

 products of the dry distillation of nitrogenous substances. 



It is worthy of remark that these substances have the property 

 of being reduced to the humid condition of putrefaction without any 

 apparent or recognisable agency of other matters, and solely by the 

 influence of atmospheric agents. While it is proved that other 

 organic substances admitting of ready decomposition, as, for 

 instance, urea, are not decomposed by the atmosphere even under 

 the most favourable conditions, if they are in a chemically pure 

 condition, the connexion of the elementary molecules of these 

 bodies is so easily disturbed by the most ordinary atmospheric 

 influences, that in the presence of water, and at an ordinary tem- 

 perature, they begin to decompose in the course of a few hours, 

 or, at all events, in a day or two. The period during which they 

 can resist these influences, that is to say, the commencement of 

 decomposition, depends greatly on the state of cohesion in which 

 the molecules occur. The substances deposited in comparatively 

 dense and insoluble masses in the animal tissues, pass far more 

 slowly into a state of putrefaction than the more finely distributed 

 substances, or those which are dissolved in water. The substance 

 of the tendons putrefies less rapidly than cellular tissue and coagu- 

 lated albumen, and the latter less rapidly than soluble albumen. 

 The products of the putrefaction of these substances have not yet 



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