304 THE AMERICAN MONTHLY [Oct. 



being fixed in the morning after tlie niglit's rest and 

 tliat of the other after a day of toil, tlie changes in the 

 cells of the brain of the lioney bee or sparrow and in the 

 spinal ganglia of the sparrow were as marked as in case 

 of artifisial fatigue. After prolonged rest then the 

 nerve cells are charged, so to speak — they are full and 

 ready for labor, but after a hard day's work they are 

 discharged, shrunken and exhausted. 



There is one more step in this brilliant investigation. 

 If in the morning after sleep and rest animals and men 

 are full of vigor, and in the evening are weary and ex- 

 hausted, how like it is to the beginning and end of life ? 

 In youth, so overflowing with vigor that to move, to act, 

 is a pleasure and continued rest a pain. But in the 

 evening of life a warm corner and repose are what we 

 try to furnish those whose work is done. How is this 

 correlated in the cells of the nervous system with the 

 states of rest and fatigue ? With a well-nourished 

 child which died from one of the accidents of birth the 

 nerve cells showed all the characters of cells at rest and 

 fully charged. In a man dying naturally of old age 

 the cells showed the shrunken nuclei and all the ap- 

 pearances of exhausting fatigue. In the one was the 

 potentiality of a life of vigorous action ; the other 

 showed the final fatigue — the store of life-energy had 

 been dissipated and there was no recovery possible. 



For the animals that possess an undoubted nervous 

 system i^robably all would admit that there is some sort 

 of nervous action corresponding to sensation ; but what 

 of living matter in the humbler forms where no nervous 

 system can be found ? That these have vital motion, 

 that they breathe, nourish themselves, grow and produce 

 offspring, none can deny. Do they have anything com- 

 parable with sensation ? As most of the lower forms 

 are minute, the microscope comes to our aid again, and 



