THE CONCEPTION OF LIFE 113 



water is taken up by the fibrils, to be given up by them again 

 when the muscles elongate. The movement of water in the 

 two types occurs in opposite senses during contraction. In 

 smooth muscles it moves out from the fibers, in striated, into 

 the fibrils. Meigs' investigation was carried out in part in 

 my laboratory, and I have been able to confirm his results 

 by the inspection of his preparations. The contraction of 

 muscles thus appears to depend on the movements of fluid 

 within the muscle, and muscular contraction is a chemical- 

 physical phenomenon. Nerve cells contain in their ncrmal 

 condition small mases, commonly designated as Nissl's bodies. 

 When a nerve cell functions these masses are used up during 

 its activity. The observations of C. F. Hodge 58 of Clarke 

 University are very convincing. He investigated the central 

 nervous system of swallows. He collected some birds in the 

 morning when they were fresh, and again others at the end of 

 the day when they were exhausted by many hours of flight. 

 He found it easy to demonstrate that the content of the nerve 

 cells was used up during the day, and that the exhausted 

 cells showed clearly the loss which they had suffered. He 

 also found that certain nerve cells in a very old man have a 

 permanently exhausted appearance and were therefore no 

 longer capable of functioning. (Mention should be added of 

 the very extensive investigation of the exhaustion of nerve 

 cells by Dr. Crile, an account of which he presented to the 

 American Philosophical Society in April, 1913.) When we 

 consider that our highest performances are functions of our 

 nerve cells, we must admit that our psychical activity also de- 

 pends upon the activity and the using up of living substance. 

 If we pass to the organs of the so-called vegetative life we 

 find similar conditions. The secretion of glands, as we first 

 learned through the investigations of R. Heidenhain, is formed 



