176 THE CHEMISTRY OF THE FARM 



same rate as the increase of surface. Thus, while the 

 oxen increase in weight from 1 — 5 "7, their surface 

 increases from 1 — 3'2, and their food from 1— 3'5. 

 The pig increases in weight from 1 — 6 "5, its surface 

 from 1 — 3*5, and its food from 1 — 3*7. In the case 

 of sheep the question is compHcated by the thick 

 covering of wool ; the weights in the table rise from 

 1 — 2*33, the surface (if calculated as in other cases) 

 from 1—1-76, and the food from 1—1-43. 



Productio7i of Work. — The work performed by an 

 animal is partly internal and partly external. The 

 internal work consists in the muscular movements 

 concerned in mastication, digestion, circulation, res- 

 piration, and other vital processes ; such work is 

 carried on even when the animal is at rest. In man 

 the whole of the blood is pumped through the heart 

 every half minute. The daily work performed by the 

 heart of a man 12 stone in weight has been calculated 

 as equal to 242 foot-tons ; that is to say, the power 

 exerted by the heart would raise 1 ton to a height of 

 242 feet. The work performed by other organs, and 

 by the muscles when merely maintaining the body 

 in an erect position, must be very considerable, but 

 has not yet been satisfactorily measured. Nearly 

 the whole of the internal work is finally resolved into 

 heat. 



As external work we may take as an example a walk 

 of 20 miles on level ground ; this to a horse of 500 

 kilos, weight (1,102 lbs.), without a load, will represent 

 an exertion equivalent to 720,976 kilogrammeters, or 

 2,328 foot-tons. During labour, about 31 per cent, of 

 the total energy developed, in the muscles appears as 

 external work, the rest will appear as heat. The tem- 



