6 BIOLOGICAL ASPECTS OF HUMAN PROBLEMS 



the brain. Descartes concluded that animals are 

 self-regulating machines, or automata, but strongly 

 repudiated this idea as applied to man. 



A striking indication of the validity of the idea 

 that the human body is essentially a machine, 

 capable of generating and expending energy like 

 machines of human invention, was furnished by the 

 highly significant discovery of the law of the con- 

 servation of energy. Faraday, the great experi- 

 mental physicist, was on the verge of this discovery, 

 but circumstances placed it within the ken of a 

 German physician, Julius Robert Meyer. Observ- 

 ant and thoughtful, this young man while on a trip 

 to a warm country noticed that the blood in the 

 veins of a patient was lighter in color than is the case 

 with the venous blood of persons in temperate or 

 cold climates. From this little observation Meyer 

 inferred that the lighter color meant less active 

 oxidation in the tissues of the body, and that this 

 lesser oxidation is just what one would expect 

 where a lesser formation of animal heat was needed 

 by the organism. In a cold climate the body would 

 be compelled to make more heat, and to do this 

 would be compelled to oxidize more intensely. It 

 flashed on Meyer that the oxidations or combustions 

 in the body must be the source of all animal heat. 

 He was thus led to look on the body as a machine, 

 and this brought him independently to exactly the 

 same conclusion as that which has been reached by 

 the physicist Joule; namely, to the doctrine of the 



