ii6 Journal of Comparative Neurology. 



Of course the records as they appear in Table VII, do not 

 furnish a series of ratios which decrease with unbroken regular 

 ity, but if the cases as they stand in the table be arranged in 

 three groups, the ratios not only decrease from the group with 

 the smallest average body-weight to that with the largest, but, 

 also in each group, fall below those for Bull-frogs of the same 

 body weight ; thus agreeing in both respects with the results 

 given in Table VI. 



III. Post-mortem Changes in the Weight of the Central 



Nervous System. 



In the study of the Bull frog we took occasion to point 

 out the remarkable increase in the weight of the brain and spi- 

 nal cord occurring when these were left in the body for twenty- 

 four hours after death. It need only be stated that experiment 

 shows a similar increase to occur in R. virescens. All our 

 specimens, however, were dissected as soon as killed, so that 

 our results are free from this source of error. 



IV. Influence of the Water Absorbed by the Living 

 Frog on the Weight of the Brain and Spinal Cord. 



When studying the Bull-frog some pains was taken to 

 show how far the weight of the frog and of the central nervous 

 system might be influenced by the amount of water present in 

 the frog, and also the manner in which this water could be lost 

 and regained. The practical outcome of these observations 

 was the conclusion that to obtain uniform results in weighing 

 frogs, they should be kept in water for some hours before they 

 are killed. 



Parallel experiments to those on the Bull-frog have been 

 made on virescens with corresponding results, so that we now 

 know this species to react like the Bull-frog. In accordance 

 with these results care was taken that the frogs used for dissec- 

 tion had been in the water for some time before they were ex- 

 amined, and thus they were in the condition of having absorbed 

 the maximum amount of water normal to them at that season 

 of the year and under the laboratory conditions. 



