GASSERIAN GANGLION! ALBINO RAT 251 



and Donaldson and Hoke ('05), Dunn ('12), Greenman ('13), 

 and Donaldson and Nagasaka ('18), but are higher than those 

 given by Greenman ('17). These last determinations were made 

 by the planimetric method, while my own determinations as 

 well as all of the others were made by direct micrometric measure- 

 ments, and this difference in technique may in part explain the 

 difference in the values found. 



I should state that in the present study the nerves were fixed 

 with a 1 per cent solution of osmic acid for five days, while all 

 the other authors fixed them for twenty-four hours only. The 

 reason for this difference was that the present author failed to 

 obtain a satisfactory staining after twenty-four hours, and thus 

 a prolongation of the tune was necessary. Whether this differ- 

 ence in technique was in any way responsible for slight differences 

 in the results is not clear. 



ON THE RELATIVE AREAS OF THE HEAD AND THE RELATIVE 

 AREAS OF THE AXIS CYLINDERS 



In regard to the ganglion cells, we have found that the rate of 

 increase in volume corresponds to the rate for the increase in 

 the area of the head surface, so far as the young animals (before 

 eighty days of age) are concerned. It is now of interest to 

 determine what relations hold for the nerve fibers, or, more pre- 

 cisely, for theu' axis cylinders. 



The increase in the area of the axis cylinder in relation to the 

 increase in the surface of the head is shown in table 14.- 



The methods of calculating the areas of the axis cylinder, as 

 well as the areas of the head, are the same as those previously 

 employed. The table shows that except in the youngest group 

 the areas of the axis cylinders increase at nearly the same rate 

 as the area of the head surface, i.e., between 16.6 grams in body 

 weight (eighteen days of age) and 230.6 grams in body weight 

 (298 days of age) ; there is good agreement in five cases. In the 

 first group, however, the ratio of the increase of the area of the 



^ It must be recognized the head surfaces really innervated by the fifth nerve 

 include not only the skin, with its specialized vibrissae, but also the cavities 

 of the mouth and nose and the teeth. These peculiarities in distribution natu- 

 rally complicate our problem. 



