THE ANIMAL AS A MOTOR. 



47 



which are the essentials to efficient action of the ma- 

 chine as a whole. The wonderful self-adjusting power of 

 the system makes these actions effective even locally ; 

 and the exercise of one member or part of the machine 

 produces increased circulation, increased degeneration, 

 and at the same time increased blood-supply and nutri- 

 tion of the part thus compelled to supply energy. 



The muscular system constitutes about 40 per cent 

 of the weight of the body, and contains blood to the 

 amount of one third this weight, or 12 to 15 per cent 

 of the whole weight of the body. The wear of this 

 muscular tissue gives rise to a demand for the nitro- 

 genous foods to supply the waste, and thus produces 

 an appetite for lean meats or for vegetable foods rich 

 in gluten. The nervous tissue, the system of inter- 

 communication and transfer of energy from part to 

 part, is also subject to wear ; and this waste is supplied 

 by the phosphatic foods, as animal brain, marrow, nerve, 

 and glandular or other white meats, and as the fruits 

 and the grain-foods, the peculiar diet of the human and 

 especially of the brain-working creature. Overuse of 

 the muscles or of the nervous system reduces their 

 powers of recuperation, repair, and general nutrition ; 

 and it is for this reason that labor and exercise should 

 be carefully restricted within those limits marked by 

 the appearance of symptoms of exhaustion. Highest 

 efficiency of the animal, as of any other machine, can 

 be permanently maintained only when the conditions 

 of maximum perfection of parts and of operation are 

 ascertained and insured. The selection of proper foods 

 is as essential to the successful maintenance and use of 

 the animal machine as the securing of good fuel for use 

 in the heat-engines ; attention to diet and the adjust- 



