350 FKAGMENTS OF SCIENCE. 



muscular tissue in 3^ days. With a fulness and preci- 

 sion of which this is but a sample did Mayer, between 

 1842 and 1845, deal with the great question of vital 

 dynamics. 



In direct opposition, moreover, to the foremost sci- 

 entific authorities of that day, with Liebig at their 

 head, this solitary Heilbronn worker was led by his 

 calculations to maintain that the muscles, in the main, 

 played the part of machinery, converting the fat, which 

 had been previously considered a mere heat-producer, 

 into the motive power of the organism. Mayer's pre- 

 vision has been justified by events, for the scientific 

 world is now upon his side. 



We place, then, food in our stomachs as so much 

 combustible matter. It is first dissolved by purely 

 chemical processes, and the nutritive fluid is poured 

 into the blood. Here it comes into contact with at- 

 mospheric oxygen admitted by the lungs. It unites 

 with the oxygen as wood or coal might unite with it in 

 a furnace. The matter-products of the union, if I may 

 use the term, are the same in both cases, viz. carbonic 

 acid and water. The force-products are also the same 

 heat within the body, or heat and work outside the 

 body. Thus far every action of the organism belongs 

 to the domain either of physics or of chemistry. But 

 you saw me contract the muscle of my arm. What 

 enabled me to do so? Was it or was it not the direct 

 action of my will? The answer is, the action of the 

 will is mediate, not direct. Over and above the muscles 

 the human organism is provided with long whitish fila- 

 ments of medullary matter, which issue from the spinal 

 column, being connected by it on the one side with 

 the brain, and on the other side losing themselves in 

 the muscles. Those filaments or cords are the nerves, 

 which you know are divided into two kinds, sensor 



