PRODUCTS OF DISASSIMILATTON. 391 



regeneration and repair after injury. We have stated, as 

 far as possible, all that is positively known of the nutrition 

 of the fully-formed tissues of the body ; but their develop- 

 ment belongs to embryology. If we were to attempt to 

 follow the processes of regeneration after injury in nerves, 

 muscles, bone, etc., we would be compelled to pass almost 

 immediately into the domain of pathology. The influences 

 of climate, respiratory activity, food, etc., have already been 

 considered under the heads of respiration, alimentation, and 

 excretion, and will be touched upon again in connection 

 with animal heat. 



Products of Disassimilation. It only remains now to 

 recapitulate briefly the mode of production of the excretions. 

 The process of disassimilation, we are aware, always accom- 

 panies nutrition, and the substances thus formed are the 

 result of the final changes of the organic constituents of the 

 tissues. As we have seen in studying the urine, the excre- 

 mentitious principles proper are always associated with in- 

 organic matter, which has passed through the organism ; 

 and while there are many effete substances that we have 

 been able to recognize, there are probably others which have 

 thus far escaped observation. It is almost futile to specu- 

 late upon the probable bearing which the discovery of new 

 excrementitious principles will have upon pathological con- 

 ditions, while there are so many, which we now know only 

 by name, their relations to the different tissues being still 

 obscure ; but if we reason from the light thrown upon cer- 

 tain diseased conditions by the fact that urea, the urates, and 

 cholesterine are liable to be retained in the blood and produce 

 certain symptoms, we may safely infer that the description of 

 new effete principles will have an important influence upon 

 our pathological knowledge as well as our comprehension of 

 physiological processes. The following are the most impor- 

 tant excrementitious matters, the relations of which to nutri- 

 tion and disassimilation are more or less fully understood : 



