52 PHYSIOLOGY AT THE FARM. 



system. On the contrary, oxidation is everywhere therein 

 in full operation. It is to be remarked, however, that the 

 proportion of oxygen in caseine is somewhat less than what 

 exists in albumen and in fibrine so that room is left for the 

 supposition, that when caseine in contact with a phosphate 

 passes into albumen or into fibrine, the deficient oxygen is 

 supplied by the deoxidation of phosphoric acid, while the 

 phosphorus set free affords the necessary atoms of phosphorus. 



In mares' milk, as in the milk of other similar mammals, oil 

 or butter, and sugar-of-milk, exist in considerable propor- 

 tion. These two proximate principles, as being destitute 

 of nitrogen, are accounted non-plastic principles that is, they 

 are incapable of supplying materials for the production or re- 

 pair of the solid fabric of the body. They have been termed, 

 in contradistinction to such proximate principles as caseine, 

 calorifacient principles that is, principles capable of sup- 

 plying animal temperature, either by being themselves slowly 

 converted into water and carbonic acid by the agency of the 

 oxygen received into the living system during respiration, or 

 by being converted into other non-azotised principles which 

 may be similarly acted on by oxygen with the production of heat. 



Oily particles plainly exercise an important influence 

 throughout the living system. When the food is destitute of 

 oily material, other non-azotised principles are certainly con- 

 verted into oil in some part of the process of digestion. The 

 oily principle in food, as the oil of mares' milk, doubtless 

 undergoes considerable changes in the various stages of diges- 

 tion, without, however, losing the essential characters of oil or 

 of its subordinate constituents. A principal change to which 

 it is uniformly subjected is that of extreme comminution of its 

 particles, as in the form of emulsion, by which change it ap- 

 pears to be able to make its way through the minutest kinds 

 of vessels known in the living economy. 





