110 PHYSIOLOGY OP THE DOMESTIC ANIMALS. 



In our study of the processes of metabolism of the animal body, in 

 which we will attempt to trace the course of the food-stuffs after their 

 entrance into the body and in their elimination as various effete products, 

 this subject must necessarily be touched upon ; the consideration of the 

 part of this subject which is at all capable of practicable application will 

 be deferred until then. 



It may only be mentioned here that the simpler an organism the 

 simpler must be the chemical changes in its constituents. Thus, we find 

 that in the elementary vegetable organisms their entire structure is made 

 up of protoplasm, which is practically almost solely albuminoid ; we have 

 then appearing chlorophyll, cellulose, starch, and in still higher forms the 

 various sugar groups, vegetable acids, alkalies, etc. In the animal body 

 a similar state of affairs holds. We may say that the body of an amoeba 

 is composed of simple albuminous matter. In the development of organs 

 we have a development of supposed chemical derivatives of protoplasm, 

 and the higher the state of development of the organism the more com- 

 plex will be the changes which have resulted from the original proto- 

 plasm. As we have already mentioned, these cell-constituents are organic, 

 nitrogenous and non-nitrogenous, and inorganic bodies. All of the sub- 

 stances which we have heretofore considered are examples of derivatives 

 or modifications of protoplasm, and as protoplasm is essentially albumi- 

 nous they are, therefore, the examples of a modification of albumen. In 

 the waste of albuminous tissues we have an immense number of inter- 

 mediary bodies, partly belonging to the various aromatic series, between 

 albuminous bodies and the simpler end products, water, carbon dioxide, 

 and urea. These bodies result from a progressive series of oxidations, 

 and will receive consideration under the subject of Nutrition. 



FERMENTS. 

 Various animal and vegetable cells will often be found to contain 

 a class of bodies which are closely allied in composition to albuminous 

 substances, since they contain carbon, nitrogen, hydrogen, oxygen, and 

 sulphur. From the fact that they are able, under certain conditions, to 

 produce reduction in the complexity of organic compounds with the 

 action of water without acting through the development of chemical 

 affinities, and without themselves undergoing change, such bodies are 

 termed soluble ferments, and are derived directly from modifications of 

 the protoplasm of the living organisms in which they originate. Al- 

 though they are apparently allied to albuminoids in their chemical con- 

 stitution, yet when purified they fail to give the proteid reactions ; and 

 although we may be pretty sure that such bodies are derived from 

 the physiological splitting up of proteids, we have no exact knowledge 

 as to their structure. When obtained dry by various processes, which 



