386 HUMAN ANATOMY 



this theory is the subject of lively and voluminous discussion, and 

 that Nissl, 1 for example, urges the inadequacy of the conception 

 on the ground that it does not account for the gray substance in the 

 strict sense. 



No one can fail to appreciate the very great importance of the 

 satisfactory conclusion of the present dispute, and earnestly desire 

 that we may obtain conclusive evidence on points involved; but how 

 ever the question of the gray matter may be settled, the enormous 

 importance of the neurone conception, and the value of it for the 

 purposes of the microscopic analysis of the nervous system, will 

 remain untouched, while our quantitative determinations, applied 

 to the neurone as we now understand it, will still have a permanent 

 value. 



Returning to the questions which are raised by the previously 

 mentioned investigations of Dubois, we require in the first instance 

 to determine the number of neurones connecting the skin with the 

 central nervous system, and to see how this number varies in the 

 different species of mammals similar in form but unlike in size. 

 There is only one animal, the white rat, on which as yet such studies 

 have been made, so that the whole field lies practically open. Should 

 we be able to get good numerical evidence in favor of the view that 

 under the conditions named above the afferent system could be 

 taken as an index of the size of the brain, it would show us at once 

 that in the laying-down of the nervous system certain proportions 

 were rather rigidly observed, and bring us to the next step, namely, 

 the determination of the influences which control those proportions 

 and the possibility of effecting an alteration in them. In the mean 

 time, there is every reason to prepare for the application of these 

 results to man, and although the programme here is simple enough 

 to state, it will involve great labor to carry it through. 



So far as the numerical relations in man are concerned, we have, 

 through the work of Dr. Helen Thompson 2 an excellent estimate 

 of the number of nerve-cell bodies in the human cortex, and through 

 that of Dr. Ingbert, 3 a reliable count of the number of medullated 

 nerve-fibres in the dorsal and ventral roots of the thirty-one pairs 

 of spinal nerves of a man at maturity. It is easy to see, however, 

 that we must get some notion of the amount of individual varia- 

 tion to which these relations are subject within the limits of one 

 race and one sex before it is desirable to attempt to learn whether 

 the difference in race or sex here plays an important role. It is to be 

 anticipated, however, that the differences dependent upon race and 

 sex will be comparatively slight, and especially so when contrasted 



1 Nissl, Die Neuronenlehre und ihre Anhanger, 1903. 



2 Thompson, Journal of Comparative Neurology, 1899. 



3 Ingbert, Journal of Comparative Neurology, 1903 and 1904. 



