986 LIFE : OUTLINES OF GENERAL BIOLOGY 



In the dark caves of Dalmatia lives the weU-known bhnd sala- 

 mander Proteus, nearly a foot long, with a white skin, a little 

 pinkish because of the blood. Its white skin is like a photographic 

 plate, as Gadow puts it, for if there is the least light it becomes 

 spotted with grey patches, and in diffuse light it becomes black. 

 The newl}'' hatched descendants of these dark parents are also 

 dark ; but this is probably because the light gets through the body 

 of the parent and influences the eggs before they are laid. In any 

 case, it depends on nurture whether a Proteus is white or black. 



II. While some developing organisms are strikingly indifferent to 

 changes in their environment, there are others which respond sensi- 

 tively, sometimes in a startling way, to changes which do not seem 

 very drastic. MacDougal's weU-known experiments of injecting 

 solutions of sugar, calcium, potassium, and zinc into the developing 

 ovaries of one of the Evening Primroses resulted in a small per- 

 centage of notably atypical individuals, which bred true to the third 

 generation. The chemical reagents introduced were not very different 

 from those which might occur naturally in the sap of the plant. 

 Among the changes induced there were not only losses and aug- 

 mentations of what was previously present, there were distinct 

 novelties which maintained their distinctness when crossed with the 

 parental strains. 



Loeb showed that it is very easy to produce a percentage of 

 fish-embryos (Fundulus) with defective eyes, by adding a minute 

 quantity of potassium cyanide to the water, or by exposing the 

 newly fertilised eggs to low temperature. That is to say, relatively 

 slight environmental changes may so alter the constitution of the 

 developing embryo that a leap is taken in the direction of blindness. 



Similarly Stockard has shown for the same fish that the addition 

 of a very minute quantity of magnesium salt to the water induces 

 in a large number of them the development of a single Cyclopean 

 eye in place of the normal two eyes. 



Such cases are to be borne in mind in connection with 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 sometimes 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 Child has more recently shown that the 

 reduction in size is associated with a remarkable rejuvenescence, and 



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