FUNCTIONS OF THE NUTRIENTS 185 



268. The critical temperature. — ^Recent investigations 

 show that under given conditions there is an air tem- 

 perature, called the "critical temperature," at which meta- 

 bolism (oxidation) reaches a minimum. If the air tem- 

 perature falls below this point thus causing a greater 

 radiation of heat from the body surface, increased oxida- 

 tion occurs. If the temperature of the air rises above this 

 point there is no diminution of oxidation but rather a 

 slight increase, hence the conclusion that there is a mini- 

 mum oxidation necessary to the maintenance of the vital 

 functions which must go on however much the demands 

 for the radiation of heat may be lessened by a rise of the 

 air temperature. It is evident then that at the higher 

 air temperatures there is an excess of oxidation above 

 that which is required for warming the animal, so that 

 some heat must be thrown off as a waste product. Which- 

 ever way the air temperature moves from the critical point 

 there is heat regulation, this being chemical for the lower 

 temperatures and physical for the higher. 



The critical temperatures for our various farm animals 

 have not been determined, so that we are not yet able to 

 draw therefrom conclusions as to the influence of given 

 temperatures upon production. The opinion is ventured, 

 however, that with animals protected by a coat of hair, 

 that are kept under comfortable winter conditions, the 

 temperatiu-e of the surrounding air does not fall below 

 the critical point. 



THE NUTKITIVE rNTEE-BELATION OF THE FOOD COMPOUNDS 

 AND THE NEED OF COMBINING THESE IN THE RATION 



As we have seen, the conclusion reached by many 

 extended and severe investigations is that the compounds 



