NUTRITION OF VARIOUS FOOD. 437 



through the effect of oxygen, which is taken into the system 

 every moment of life by means of the organs of respiration. 

 But no part of that oxygen remains in the body ; it is expelled 

 in the form of carbon and hydrogen, by exhalations from the 

 skin, and the ordinary evacuations. The expenditure of carbon 

 and hydrogen is increased by labor or exercise in an equal 

 ratio as the number of exhalations are accelerated by that ex- 

 ercise. By this process the fat and muscular fibre are constant- 

 ly in a state of exhaustion and renewal, and are supposed to be 

 thoroughly renewed in the course of six or seven months ; de- 

 pendent, however, upon the amount of labor, and the uninter- 

 rupted health of the animal. The more expeditiously this 

 renovation of the system takes place, the more perfect will be 

 the condition of the subject. It is therefore evident that the 

 nutritive matter supplied by the food must exceed the exhaus- 

 tion which takes place in young animals, to occasion their 

 growth and increase the development of muscle and other tis- 

 sues, and with adults it must be equivalent with the exhaustion 

 to maintain the animal in a normal state. 



It has been ascerta'ined that such vegetable food as afibrds 

 nourishment to animals abounds most with nitrogen ; and that 

 they require the least of those kinds which contain the largest 

 quantities. But here it must be observed there is a limit to the 

 presentation of food abounding too profusely with nutritive 

 properties, which will speedily affect the animal partaking 

 thereof The blood-vessels will become distended, and other 

 channels overcharged with an excess of their fluid ; and upon 

 the slightest appearance of the symptoms which indicate a dis- 

 ordered state of the circulation, unless medicines are presented 

 which are calculated to relieve the system from the accumula- 

 tion, aided by temporary abstinence, and indeed change of 

 food, the health of the animal is sure to suffer. 



Professor Playfair, who has made experiments on the quan- 

 tity of nutritious matter contained in different kinds of food 

 supplied to animals, found that in one hundred lbs. of oats, 

 eleven lbs. represent the quantity of gluten wherewith flesh is 

 formed, and that an equal weight of hay affords eight pounds 

 of similar substance. Both hay and oats contain about 

 sixty-eight per cent, of unazotised matter identical with fat, of 



