486 PHYSIOLOGY AT THE FARM. 



secretion go on by an inner directive movement, independent 

 of the man's will. On these operations a large amount of 

 work is expended. We can calculate it with accuracy in the 

 case of the human heart. This important organ is continually 

 propelling blood with force through the arteries, never ceasing 

 day or night in its labours. If we suppose that the efforts 

 used by it in propelling blood were all concentrated in raising 

 its own weight, then its daily work is represented by the aston- 

 ishing number that it might raise its own weight about ninety 

 miles high." * Thus the heart's action constitutes a principal 

 part of what in the above quotation is called vital work : it is 

 of the same character in common quadrupeds, and also in other 

 parts of the animal kingdom as in man. What is specially 

 termed " heat work," is that part of the eremacausis or slow 

 combustion which supplies the heat that replaces the temper- 

 ature lost by the living body, owing to the medium in which 

 it lives being colder than itself. " Mechanical work " is the 

 power with which living bodies operate on things without, as 

 when a labourer is engaged in digging a drain, or a horse is 

 employed in dragging a stage-coach. " Mental work " is the 

 exercise of thought, said to be the source of a high expendi- 

 ture in man, however limited in common quadrupeds and 

 the like. 



It cannot be repeated too often that while an animal is sta- 

 tionary in point of weight, the ingested matter, in a given time, 

 must be equal to the egested matter ; that is, that the food must 

 be of the same absolute quantity as the excretions in the period 

 referred to. The excretions which require to be taken into 

 account in making this comparison are essentially the carbonic 

 acid gas thrown off in respiration, the urea as a type of the 

 urinary excretion, and the feculent discharge from the bowels. 

 There is, then, as just stated, during the actions of life, and 



* ' Good Words, ' February 1865. 



