THE ANIMAL A MACHINE 157 



with a spark plug in it. We can observe that the lid will 

 blow off if we pour hot gasoline into the box, allow it to 

 vaporize, and send a spark from an induction coil through 

 the spark plug. The explosion, we know, occurs because 

 gasoline burns in the air. In a mixture of gasoline vapors 

 and air, there must be a very rapid spreading of the flame, 

 in other words, an explosion. By experimenting with such 

 simple devices we find the basis of the underlying action 

 and can understand how continuous motion can be pro- 

 duced by a series of explosions set off by a timing device in 

 rapid consecutive order. We can grasp the importance of 

 the entire complicated mechanism of an appropriately 

 constructed gasoline motor. 



Do we know anything as definite about the mechanism of 

 muscular contractions? We certainly do not, but the com- 

 parison with the motor shows us the cause of our ignorance: 

 our lack of knowledge is to be blamed on our inability to 

 make muscles, or flesh, artificially. 



2. AMOEBA AND ITS MOVEMENT 



Since it is impossible to make a real muscle artificially, 

 and thus to study the mechanism of its action, we have to 

 find some other way to free ourselves from our ignorance. 

 We have to start the investigations on a simpler type of 

 living thing. As such we select those small animals which 

 consist of one single cell, the so-called protozoa, the 

 lowest type of animal. They constitute the major portion 

 of the fauna in midocean, but are found also on land, in 

 ponds and rivers; in short, everywhere. 



The simplest of these primitive creatures are the Amoe- 

 bae, one of which is the Amoeba Proteus. This animal can 

 be found by searching, with the aid of a microscope, in the 

 water of stagnant pools. It is only | of a millimeter in 

 diameter, glassy looking and irregularly shaped, invisible 



