Henry H. Donaldson 



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On comparing the averages for the percentage deviations in these two columns 

 we find the average for the excess 3.4 per cent., while that for the deficiencies is 4.1 

 per cent. — results practically the same as those obtained for both sexes in Table I. 



TABLE VII 

 Showing the percentage deviation for the female leopard frogs entered in Table III. 



Average deficiency, 2.9 per cent.; average excess, 3.9 per cent. 



In this case the results are similar to those found in the female bullfrogs, except 

 that the larger average percentage is on the excess side. 



From these observations we conclude that in normal summer frogs of both sexes 

 it is possible to calculate, with a high degree of accuracy, by the formulae here 

 employed, the absolute weights of the central nervous system. 



Should others be inclined to test the correctness of these results by repeating the 

 observations, it will be necessary carefully to avoid the sources of error which have 

 been here enumerated, namely, the limitations of small size, the effect of season in the 

 spring and autumn, and of the nutritive condition of the frog, as represented by starva- 

 tion on the one hand, and the abnormal absorption of water or of drying on the 

 other. 



With these results in hand it is natural to seek for an interpretation of the 

 formula which has been given in order to correlate it in detail with the changes which 

 we know are going on in the central nervous system of the animals under examination. 

 In the first place, the changes in the central nervous system, which the formula expresses, 

 must take departure from the conditions which are present in the smallest frogs exam- 

 ined. In such a frog the central nervous system is composed of the supporting struc- 

 tures, neuroglia and ependyma, together with the blood and lymph vessels, and the 

 nerve cells. These last form by far the greatest part of the substance. The nerve 

 cells, or neurones, may be divided into those which are immature and those already 



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