ACTIVITY OF THE ALBINO RAT 39 



(Figs. 13 and 14), followed in each case by a noticeable decline 

 in activity and weight. This decline was followed by another 

 rise in activity and weight at about the age of 1 7 months. Again 

 a similar rise though not so marked is noticed at the age of 23 

 months. These changes are often largely due to changes in 

 food. Previous to and during each of these increases food 

 richer in protein was fed than during the periods of decline. 

 These changes in weight are not, however, always due to changes 

 in food. Many other conditions enter to bring about these 

 results, as they often occur when their diet is as nearly constant 

 as possible. The following example will suffice. A very notice- 

 able depression is seen ending the 21st month. During the two 

 months previous to this date workmen were busy making repairs 

 incident to the earthquake of April 18, 1906. These repairs 

 necessitated a great deal of pounding and confusion in the 

 adjacent room, which was connected by ventilators to the 

 experiment room. Old plastering had to be removed and new- 

 put on, which caused a great deal of dust and noise. In this 

 case I think it was the confusion and dust that caused the 

 rapid decline in activity and weight as the diet had been such 

 as to maintain uniformity in these respects. 



I attribute the difference in weight between the control and 

 exercised rats to the fact that the control rats did not have a 

 ready means of exercise. They could give but a jump or two 

 before they would be at the end of their run. In other words 

 there was nothing to stimulate exercise. As a result the energy 

 which would have been expended in exercise had favorable 

 conditions been offered was used in growth. The experience 

 of stock raisers corroborates this. Whenever they wish animals 

 to increase in weight rapid ly they pen them up. They have 

 found that the same amount of food will fatten slowly or not 

 at all when the animals are permitted a large range. This same 

 idea is also advanced in poultry raising and production. It 

 seems to me from the experiments on the albino rats that there 

 are good grounds for such ideas. However, one must not lose 

 sight of the product desired. If weight and rapid growth are 

 desired feed the animal in close confinement. If agility and 

 ability to perform work and endure fatigue are wished allow 

 the animal considerable range which allows normal daily exercise. 



