CHAPTER XII 



Experimental biology, mechanism versus vitalism continued. 

 Tropisms, instincts and intelligence. Hormones. Arti- 

 ficial fertilization. 



But can physics or chemistry explain the as yet unknown 

 processes of nervous action; the bewildering perplexity of 

 the instinct of bee or bird or beast, or the yet more amazing 

 intricacies of human thought? To answer this question, as 

 indeed to solve any of the problems of living matter aright, 

 it is essential that we turn to the lowest rather than to the 

 highest organisms, to those which present to us in their 

 simplest terms, all the fundamental processes of the living 

 thing. If the extended process or pseudopodium of an Amoeba, 

 one of 'the simplest types of living things, be touched with a 

 finely drawn out thread of glass, the process is retracted and 

 the direction of movement of the animal is altered thereby. 

 If on the other hand Amoeba comes in contact with some 

 object, which serves as food, it reacts positively toward it, 

 thrusting out its processes and engulfing the object. Further- 

 more Amoeba can pursue its food, so that to the observer it 

 seems as if this tiny bit of protoplasm, so small that the 

 largest specimens appear to the naked eye as mere specks of 

 white, were endowed with a sort of primitive intelligence. 

 This pursuit of food has been described by Jennings as 

 follows: "I had attempted to cut an Amoeba in two with the 

 tip of a glass rod. The posterior third of the Amoeba, in the 

 form of a wrinkled ball, remained attached to the body only 

 by a slender cord, the remains of the ectosarc. The Amoeba 

 began to creep away, dragging with it this ball. I will call 

 this Amoeba a, while the ball will be designated b. A larger 

 Amoeba (c) approached, moving at right angles to the path 

 of the first Amoeba; its course accidentally brought it into 

 contact with the ball b, which was dragging past its front. 

 Amoeba c thereupon turned, followed Amoeba a, and began 

 to engulf the ball b. A large cavity was formed in the an- 

 terior end of Amoeba c, reaching back nearly or quite to its 

 middle, and much more than sufficient to contain the ball b. 

 Amoeba a now turned into a new path; Amoeba c followed 

 (4). After the pursuit had lasted for some time the 



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