252 PHYSIOLOGY AT THE FARM. 



like the ox for slaughter, by rendering the solids soft, tender, 

 and free from toughness. The essential difference appears to 

 be that an arterial plethora or fulness of blood is to be culti- 

 vated in the case of the horse, while a venous plethora is to be 

 promoted in that of the ox. 



Respiration, "When an animal solid, consisting of oxygen, 

 hydrogen, carbon, and nitrogen, is decomposed in the presence 

 of oxygen, it can readily be understood to afford carbonic acid, 

 water, and some compounds of an ammoniacal nature, or allied 

 in composition to ammonia ; as urea, the essential saline principle 

 of the urine. When, on the other hand, an organic product, free 

 from nitrogen such as sugar derived directly from the aliment, 

 or obtained by the transmutation of starch or oily matter, 

 such as fat derived from the food or absorbed into the blood 

 from the adipose tissue is decomposed in the presence of oxy- 

 gen, it affords carbonic acid and water. These two decompo- 

 sitions namely, the decomposition of non-azotised matter and 

 the decomposition of azotised matter are unceasingly taking 

 place within the living body, and are indeed essential to its 

 continued existence, If these two decompositions did not go 

 on at all times, the blood would become loaded with the debris 

 of the solids, so as to be no longer fit to maintain the vital 

 properties of the component tissues of the organs essential to 

 life, and the body would begin to cool down to the temperature 

 of the surrounding medium. 



It belongs to the function of respiration to supply the 

 oxygen required in these two indispensable decompositions. 

 Of these decompositions, that of azotised matter is doubtless 

 altogether the most important ; for in countries where the heat 

 of the climate at times equals the natural temperature of the 

 animal body, the decomposition of non-azotised matter, on 

 which chiefly the production of temperature depends, becomes 

 superfluous ; but that by which the purification of the blood 



