AN INTRODUCTION TO THE STUDY OF GROWTH. 30 



the conditions in many ways. Those in the larger 

 amount of water were the larger, and beginning with 

 those grown in the least quantity, which were the 

 smallest, they could be arranged in a series increasing 

 in size, according to the quantity of water in which they 

 had been placed. The explanation of these suggestive 

 results is, to say the least, obscure, but it must ultimately 

 rest on variations in nutrition, which may be influenced 

 by the amount of activity of the animal and the diffu- 

 sion of its own waste products, which act as poisons, and 

 which would be effective in proportion as the quantity 

 of water was small. In a recent account of some con- 

 ditions which modify growth, Bizzozero states that cell 

 division is not stopped by starvation, though it may be 

 thus decreased in intensity, and that inanition may even 

 rouse dormant cells to the act of division. In the ear 

 of the rabbit, hyperaemia causes increased cell multi- 

 plication, together with increase in size of the ear ; and 

 the same result may be effected by high temperature. 

 Conversely, low temperature retards in a most remark- 

 able manner the increase of the growing ear. When, 

 however, the low temperature is replaced by a normal 

 degree of heat, the ear previously dwarfed overtakes the 

 one which has been left under the usual conditions, and 

 very soon becomes equal to it in size. 1 By the aid of 

 the nervous system the response of an animal to condi- 

 tions influencing growth is modified in various ways. 

 Among paired glands the removal of one causes in- 

 creased size of the other. Here growth is compensatory. 

 On the other hand Samuel found that the renewal of 

 the feathers in a pigeon's wing was modified by dis- 

 turbances of the circulation, and also that when the 

 disturbance was practised on one side only it caused 

 an arrest of growth in the feathers on both sides, 

 1 Bizzozero, Wien. Med. Blcitt., 1894. 



