INFLUENCE OF ENVIRONMENT 87 



bears from small and warmed cages to the greater 

 exposure and freedom of the Mappin Terraces at the 

 London Zoological Gardens have improved the 

 quality and thickness of the fur in a single season. 

 Plants that usually bear thin and hairy leaves pro- 

 duce smooth and fleshy leaves almost immediately 

 under the influence of increased moisture and 

 salinity, and the structure of water-shrimps and 

 molluscs varies with the saltness of the water in 

 which they are reared. The nature of the food 

 affects the size, appearance, structure and fertility 

 of many plants and animals. The circumambient 

 media are the active agents in producing the average 

 character of most populations, but we are apt to 

 overlook them, partly because of the unsettled con- 

 troversy as to the inheritance of acquired characters, 

 and partly because we fail to allow for constant 

 agents, and so attribute to nature what is due to 

 nurture. 



The conditions of the environment, which differ 

 from nation to nation, act directly on each generation. 

 We may suppose even that they have an influence 

 on children before birth. Alcohol, cocaine, and many 

 bacterial poisons and diseased conditions are known 

 to affect the embryo through the blood of the mother. 

 The influence of the nutrition of the mother has 

 probably much to do with determining the physio- 

 logical rhythm of the child. Some years ago great 

 notoriety was given to a theory that the sex of an 

 unborn infant could be determined by regulating the 

 quantity of sugar in the tissues of the mother, and 

 although enquiry did not confirm this particular 

 suggestion, there is no doubt that the mother is much 



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