The Living MacJiinc 283 



"Whatever the answer to the riddle of life may ultimately 

 be it is at least certain that our present most hopeful line 

 of attack lies in the, at least partially known, fields of physics 

 and chemistry, rather than in the unknown metaphysical one 

 of ''vital principles," "entelechies" and other hypothetical 

 factors. What information then does the bio-chemist have 

 to give us which may help us in the solution of our problem ? 



The writer once accompanied a class of school-boys through 

 a Colorado mine. On the mine track stood a string of empty 

 cars, and one of the boys asked the conductor of the party 

 what kind of fuel they used for their engines in the mine. 

 "Hay," replied tlie conductor, which somewhat puzzled the 

 boys, until they learned that mules furnished the motive 

 power for the cars. One of the earliest speculations of physi- 

 ologists was regarding the nature of animal heat. Some 

 animals (birds and mammals) have a constant body tempera- 

 ture which is usually higher than that of their surroundings. 

 "What is this heat, and whence does it come?" the early 

 investigators asked themselves. It was at first supposed 

 that heat was a substance which entered and left the body 

 in some unknown way. Toward the beginning of the eight- 

 eenth century speculation began to call experiment to its 

 aid, and Mayow, Boyle and Priestley tried keeping small 

 animals in closed chambers, with the result that they soon 

 died. They also tried introducing lighted candles into similar 

 chambers and found that just as the "flame of life" was 

 soon extinguished, so too the candles went out, if denied air. 

 They further found that an animal could not live so long in 

 a jar in which the air had been exhausted by a burning 

 candle as in one in which the air was fresh; and vice versa 

 the candle would not burn where an animal had exhausted 

 the air before it, nor would one animal live as well in a 

 chamber formerly occupied by another, or one candle burn 

 as well where another had been previously burned, as in one 

 containing air which had not been used up previously. These 

 experiments led them to suspect that the breathing of the 

 animal and the burning of the candle were similar processes. 



Soon after followed Priestley's discovery of oxygen which 

 he called by the sophisticated title of dephlogisticated air, 

 from the Greek word phlogiston or inflammable. Now fol- 

 lowed Lavoisier's discovery that when a candle was burned, 

 or an animal breathed, the oxygen or dephlogisticated air of 

 Priestley, which formed one-fifth of the volume of ordinary 

 air, was converted into what was formerly known as "fixed 

 air," a compound of carbon and oxygen. Lavoisier now 

 assumed that the heat of the animal body was produced in 

 a manner analogous to that of the burning candle, namely 



