Donaldson and Schoemaker, Absorption of Water. 185 



yielded the higher weight of the cord. It appears therefore, 

 that in the two independent series of observations, made by 

 similar methods but by different persons, the frogs dissected 

 during the same months were alike in the weights of their spinal 

 cords, while those dissected during different months differed. 

 If, then, season is one determining factor, we can see without 

 entering upon the details that frogs of a given weight or of a 

 given length, have in the spring and summer heavier spinal 

 cords than in the autumn, the difference in favor of the 

 former group being sometimes as great as 25^0. 



The cause of this excessive weight of the spinal cord in 

 the spring frogs is still to be investigated, although one thinks 

 of course, of an excess of water as in the main responsible for 

 it ; but that can only be determined by further investigation. 

 Pursuing the usual methods of work, this investigation has ex- 

 tended over several months, but we have only recently appre- 

 ciated that by thus extending it, we were working in the different 

 months from midsummer to autumn, with frogs normally dis- 

 similar in the absolute weight of their spinal cords and in their 

 powers of absorbing water, and hence giving us results which 

 probably show a smaller range than would have been found if 

 all the frogs had been examined during the season when they 

 were capable of the maximum absorbtion. 



The use to be made here of the relations just described is 

 as a basis for comment on the records about to be given so that 

 they may be more fairly compared. 



What has been said should be understood to apply strictly 

 only to the species of frog which we have used. It probably 

 applies in some degree to other species also, but thus far only 

 casual experiments on the bull-frog {Rana catesbia7id) have been 

 made. It is possible of course, that other species, more fixed 

 in their habits i. e., not wandering so far from standing water, 

 may possessess a different curve representing their cord weight 

 and its powers of absorbtion, but it seems probable that all 

 frogs in this neighborhood pass through a similar seasonal 

 change. From this it follows, of course, that in undertaking 

 investigations like the one here described, only frogs of the 



