75 2 THE POPULAR SCIENCE MONTHLY. 



tions. But the functions of a vital organism are themselves vital. 

 What, then, is the meaning of "vital" as applied to a function? 

 Fortunately, the answer is not difficult. " Life," says Kiiss, the dis- 

 tinguished Strashurg physiologist, "is all that can not be explained 

 by chemistry or physics." Guided by such a definition the work of 

 the physiological investigator is simple. He has only to test each sepa- 

 rate operation which he finds going on in the organism, and to declare 

 whether it be chemical or physical, If it be either, then, since each 

 function is non-vital, the entire organism must be non-vital also. Hun- 

 dreds of able investigators, provided with the most effective appliances 

 of research, are now in full cry after the life-principle. Naturally, a 

 vast amount of collateral knowledge is accumulated in the process. 

 The quantitative as well as the qualitative relations of things are fixed 

 and many important facts are collected. 



With the object in view thus clearly defined, we are not surprised 

 that great progress has been made. A vital process, like the catalytic 

 ones of the older chemistry, was found by such research to be simply 

 a process which, for want of sufficient investigation, is not yet under- 

 stood. While therefore, undoubtedly, much work yet remains to be 

 done in the realm still called vital, the prophetic vision is already 

 bright which will witness the last traces of inexplicable phenomena 

 vanish and the words expressing them relegated to the limbo of the 

 obsolete. 



As a first result of recent work, the living organism has been 

 brought absolutely within the action of the law of the Conservation of 

 Energy. Whether it be plant or animal, the whole of its energy must 

 come from without itself, being either absorbed directly or stored up 

 in the food. An animal, like a machine, only transforms its energy. 

 Lavoisier's Guinea-pig placed in the calorimeter gave as accurate a 

 heat-return for the energy it had absorbed in its food as any thermic 

 engine would have done. But the parallel goes further. The me- 

 chanical work of an engine is measured by the loss of its heat and not 

 of its substance. So the mechanical or intellectual work of a living 

 being is measured by the amount of food rather than the amount of 

 tissue which is burned. The energy evolved daily by the human body 

 would raise it to a height of about six miles. 



But, besides heat, work may be the outcome of the organism ; and 

 this through the agency of the muscles. Their absolute obedience to 

 mechanical law in their mode of action has been admirably established 

 by Haughton. The work a muscle does, it does in contracting. It 

 is to the mechanism of muscle-contraction that we are indebted for 

 another illustration of our subject. 



When work is done by a muscle in contracting, three changes are 

 observed to take place in its tissue : First, there is a loss of its electric 

 tension ; second, there is an evolution of heat in it ; and, third, carbon 

 dioxide appears there, and its reaction, before neutral, becomes acid. 



