184 Journal of Comparative Neurology. 



In this series of changes between the appearance of the 

 frog in the spring and his disappearance in the autumn, the re- 

 action of the entire frog towards water appears to unckrgo a 

 pecuh'ar though regular alteration. In general, we t^ct tlic im- 

 pression that the frog contains a larger amount of water during 

 the spring and early summer, and that this amount decreases 

 gradually up to the time of hibernation, during which time the 

 amount of water is at a minimum. As we have shown else- 

 where (i, 2), the water taken up by the frog can be entirely 

 absorbed through the skin alone, and in the absence of any 

 direct observations showing that the \yater is taken by the 

 mouth, we may conclude that the skin is practically the only 

 channel by which the water passes into and out of the tissues. 



What the conditions are which determine when the living 

 frog shall take up more water and how much shall be absorbed, 

 it was not our purpose to determine. Though it appears very 

 probable that the power of nervous system at least to absorb 

 water under the conditions offered by these experiments varies 

 with the season. We wish here merely to insist on the normal 

 existence of a rhythmic variation in the amount of water and 

 on the fact that this variation affects the weight of the spinal 

 cord. Our attention was turned to the normal variation in the 

 weight of the nervous system and its percentage of water, by 

 the fact that the present series of observations were made 

 mainly in the latter portion of the summer of 1900. When the 

 weights of the fresh spinal cord of this present series were com- 

 pared with those which had been taken a year previous (2) and 

 which were in a large measure obtained during May and June 

 (though some of the observations were made later), we found 

 the curious fact that the earlier records gave higher weights, 

 the frogs compared being of the same body-weights and lengths. 

 On comparing the few observations which had been made dur- 

 ing the same months in the two series, we found that the cord 

 weights under these conditions were very similar. On exam- 

 ining the earlier paper just alluded to, for cases where frogs of 

 the same weight had been dissected both in the spring and in 

 the autumn, we found that within this series the spring frogs 



