The Fourth Approach 

 THE ANIMAL A MACHINE 



1. ENERGY OUTPUT AND MECHANISM OF ACTION 



Living animals are often compared to machines. Such a 

 comparison suggests itself to the people of a machine age such 

 as ours. It is customary nowadays to inquire how many 

 miles per gallon the new Ford will do. In times past no 

 one thought of asking how many miles per pound of oats 

 the good old horse would make. Some modern slanderers 

 have spoken of the horse as an oats motor, and science has 

 already attacked the suggested problem. 



The customary scientific approach is to perform measure- 

 ments on single muscles. If a muscle works, it burns glu- 

 cose, a special kind of sugar — just as an automobile motor 

 burns gasoline. To determine the efficiency of the "muscle- 

 machine" scientists preferably experiment on muscles dis- 

 sected from frogs or other cold-blooded animals. These 

 muscles contract even after they have been removed from 

 a living animal. A contraction occurs when an electric 

 current is passed through the muscle, or when it is pinched, 

 or suddenly heated, or touched with an irritant chemical. 

 The muscle is held at one end and attached to a weight at 

 the other. By contraction, it lifts the weight. The 

 amount of sugar burned while lifting the weight can be 

 determined by chemical analysis and the efficiency thus 

 calculated. Expert scientists have perfected such measure- 

 ments to an almost incredible degree. They have won 

 thereby high scientific awards, since this line of work seems 

 to have a strong appeal. It is generally taken for granted 

 that we only need to collect data concerning the "living 

 machine" in order to understand its mode of action. 



It is difficult to see, however, how this expectation can be 



155 



