THE INFLUENCES OF NURTUEE 93 



of the epidermis, a callosity, an honourable mark of 

 hard work. The schoolboy sometimes has one on his 

 thumb during the season of playing marbles. It is a 

 positive functional modification, a direct reaction to a 

 peculiarity in function. Yet a wart may arise that 

 simulates a callosity, but cannot be referred to any 

 cause operating from without. 



A Russian naturalist, Ogneff, shut up some goldfish 

 in total darkness for three years, taking care to give 

 them plenty of food and plenty of room. At the end 

 of the three years they were quite blind ; the rods and 

 cones (the percipient elements) of the retina had disap- 

 peared. This was a negative modification, directly con- 

 nected with the absence of light and the cessation of 

 vision. A certain amount of functioning seems to be 

 nefeessary if a normally active structure is to retain its 

 position, its architectural stability. 



A Japanese investigator subjected white rats to hard 

 exercise for 90 to 180 days, which is comparable to a 

 period of 7 to 14 years in man, for the length of life 

 in the white rat is about three years. What was the 

 result? There was an increase in the weight of the 

 heart, kidneys, and liver, on an average to about 20 

 per cent. This is an illustration of a modifying influ- 

 ence affecting several parts of the body in a similar 

 way. 



It has been shown (by Semper and de Varigny) that 

 the young of the fresh-water snails (Lymnceus) will 

 develop into dwarfs in an aquarium where aeration is 

 abundant, and food likewise, where indeed everything 



