400 TRANSMISSION 



interruption at the point where the nerve connection is severed. 

 The thread serves perfectly to carry the impulse over from the 

 last segment of the anterior piece to the first of the posterior. 

 The unavoidable conclusion is that at least from this point back- 

 ward each segment derives its impulse not from nerve fibers but 

 from the segment just ahead ; in other words, that the motion of 

 one part becomes a stimulus to appropriate action in a neighbor- 

 ing part. 



It is reported that Ribbert transplanted a milk gland to the 

 ear of a guinea pig, and that when the individual became preg- 

 nant the gland commenced to secrete milk. Whatever the 

 nature of the stimulus, it was clearly independent of nerve 

 impulse. 1 



It is a well-known fact that if an ant be removed from its 

 nest for a time and then put back, it will be critically examined, 

 but will be received again ; if, however, a stranger ant be intro- 

 duced, it will at once be attacked and killed. How is the differ- 

 ence detected ? This question is largely answered by the fact 

 that, if the ant belonging to the nest be smeared with the juices 

 of a crushed stranger, it will at once be attacked and killed as 

 would the real stranger. 2 Clearly it is by the odor that the ants 

 detect the difference, much as the dog recognizes his master in 

 daylight or in the darkness, or follows a trail along a crowded 

 street. All this shows that even a slight cause, like odor, may 

 serve to start the operation of a train of most remarkable re- 

 flexes, which, once started, proceeds automatically, each act 

 operating as a stimulus to the next. 



This fact is further illustrated in the case of dogs deprived of 

 large portions of the nervous system. Individuals that have 

 lost the spinal cord " almost up to the medulla " may live for 

 years and perform all normal functions. 3 



Goltz entirely removed both hemispheres of the brain from a 

 full-grown dog. The first effects of so violent an experiment are 

 apparently disastrous, but if skillfully done the shock soon sub- 

 sides and all normal ftmctions of the body proceed as before. 

 That is, the animal performs the external acts of eating, urina- 

 tion, defecation, etc., the same as when in possession of the brain, 



1 Loeb, Physiology of the Brain, p. 206. 2 Ibid. pp. 220-221. 3 Ibid. p. 43. 



