ARTICLES 393 



external forces acting on the animal as passive material, but 

 rather as the expression of the response or reaction of the animal 

 in its endeavour to adapt itself to the changed circumstances. 

 This may be made quite clear to the reader unversed in zoology 

 by considering a very well known phenomenon, viz. the two 

 kinds of sunburn. 



The observant onlooker at one of our seaside resorts would 

 be struck by the fact that summer visitors exposed to an un- 

 wonted glare of sunshine exhibit two different types of effect. 

 Some become scarlet and suffer a good deal of pain ; the skin 

 peels off, leaving raw surfaces, which only slowly heal. In 

 others, however, the skin acquires a deep brown colour, and 

 there is no pain and little or no peeling. The first exemplify 

 the direct effect of sunlight as a destroyer of tissue ; the rays 

 of high frequency cause necrosis of the epidermal cells, and 

 pain and inflammation result ; but in people belonging to the 

 second category, the body reacts to the unwonted stimulus of 

 the bright light ; cells laden with dark pigment migrate to the 

 surface, and screen the underlying tissue from the deleterious 

 effect of the rays. In a word, such people become used to the 

 bright light and suffer no further inconvenience ; and by the 

 inheritance of acquired characters, we mean simply the inherit- 

 ance of the effects of use and disuse. The effects of disuse are, 

 of course, the converse of the effects of use, and are even better 

 known. If a person becomes slightly lame in one foot, so that 

 he acquires the habit of resting mainly on the other, the muscles 

 on the unused side will in the course of a few years dwindle so 

 much that the one leg becomes a feeble copy of the other. 



The theory of the inheritability of the effects of use and 

 disuse is usually termed Lamarckism, because it was precisely 

 formulated by Lamarck in his Zoological Philosophy , from which 

 the following sentences are taken (English translation by 

 Elliot) : 



(i) Every fairly considerable and permanent alteration in 

 the environment of any race of animals works a real alteration 

 in the needs of that race. 



(2) Every change in the needs of animals necessitates new 

 activities on their part for the satisfaction of those needs, and 

 hence new habits are formed. 



(3) Every new need which necessitates new activities for its 

 satisfaction requires the animal either to make more frequent 

 use of some of its parts which it previously used less, and thus 

 greatly to develop or enlarge them, or else to make use of entirely 

 new parts to which the new needs have imperceptibly given 

 birth by inner feeling. 



(4) All the acquisitions or losses wrought by nature on 

 individuals through the influence of the environment in which 



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