xx THE INFLUENCE OF ENVIRONMENT 405 



man and mammals where even slight extrinsic or 

 exogenous changes in the blood of the mother may affect 

 the development of the unborn offspring living in intimate 

 symbiosis with her. It is very important to realise 

 the difficulty of distinguishing between what is due to 

 inherited nature and what is due to some peculiarity in 

 ante-natal nurture. 



The effect of negative nurture on the individual is some- 

 times very remarkable. It is well known that certain 

 simple worms (Planarians) can be starved for months 

 without fatal effects. They become smaller and smaller, 

 living on their own internal resources. Some of their 

 cells disappear altogether and others are greatly reduced 

 in size. This is an old story, but Prof. Child has recently 

 shown that the reduction in size is associated with a 

 remarkable rejuvenescence, and that the vital processes 

 are quickened. The starveling becomes young again 

 surely a quaint biological justification of asceticism. 

 Many similar facts are given in Child's recently published 

 book on Senescence and Rejuvenescence. 



And what is true of nutrition is true of other factors 

 in nurture ; they alter the punctuation of the life-cycle. 

 A herring's egg in the sea hatches in about a week ; put 

 it in a refrigerator, and the development is slowed down 

 so that the egg takes fifty days to hatch. 



(3) Without assuming that a peculiarity of the body 

 acquired as the direct result of a peculiarity in nurture 

 can be as such or in any representative degree entailed 

 on the offspring, of which there is no convincing proof, 

 we may recognise that nurture may be of considerable 

 importance to the race in indirect ways. The modifica- 

 tion may give the individual a life of conspicuous success 

 or failure, which may result in a subsequent increase or 

 decrease in the numbers of the type which is modified, 

 thus obviously working for both good and ill to the race. 

 Vigour acquired by open-air exercise gives a man resisting 

 pow r er against infection ; it may keep bad constitutions 

 alive ; it may also keep good constitutions from being 

 gratuitously weakened. Reduction of the likelihood of 

 infection will also w r ork both ways. Moreover, organisms 



