Hardesty, Medii/la Spinalis of tJie Elephant. 175 



Table IV. Given for comparison of the actual and relative areas of the 

 substantia grisea, the substantia alba, and the areas of the sections of the cell- 

 bodies as found in the transverse sections of the largest segment of the intu- 

 mescentia cervicalis of the animals named. The areas of substantia grisea re- 

 corded in columns i and 6 are brought forward from Table III, under which 

 the method of obtaining the areas is described. The area of the substantia 

 alba (column 3) is obtained in each case by subtracting the area of substantia 

 grisea from the area of the entire section (column 5, Table III). The area of 

 the section of the cell-body (column 5) is obtained for each entry by consid- 

 ering the cell-body as a circle with a radius of one half the average mean diam- 

 eter of the cell-body as recorded in column i of Table III, and reducing the 

 result obtained to terms of sq. mm. The ratios given in columns 2, 4, and 7 

 are obtained for each specimen by the division of the first factor mentioned- in 

 the heading of the column into the second, and thus represent the relative 

 amounts of the two factors. For example, in colum 2, for the elephant the 

 ratio of the area of substantia grisea (column i) is to the area of the entire 



section (column t;, Table III) as ^^^"^ or as I is to 5.6. In other words, the 



76.5 

 area of the entire section is 5.6 times the area of the substantia grisea con- 

 tained in it. 



All particulars found in material from a single individual 

 may not be common to the class. Certain of the details given 

 in Table IV might have been materially altered had a number 

 of individuals been investigated in each case instead of one and 

 the records in the Table computed from averages from different 

 individuals. Since this would have been an extremely labor- 

 ious task, certain assumptions must be allowed. 



Assuming, then, that what is true for the individual is true 

 for the class, attention is called to the columns of Table IV as 

 giving reasons for the following statements : 



I. The area of the substantia grisea (col. i) in the trans- 

 verse section of the intumescentia cervicalis decreases gradually 

 with the decrease of the size of the animal, and the ratios of 

 the area of substantia grisea in section to the area of the en- 

 tire section are similar for animals approaching each other in 

 size of body. 



The decrease is not a regular one. The ox, with a greater 

 average body weight than the horse and a larger cell-body at this 

 level, gives a section both whose entire area and the area of whose 

 substantia grisea is less than that of the horse. The former defi- 

 ciency on the part of the ox is shown in columns 2 and 3 to be 

 entirely due to the smalleramount of substantia grisea, forthe area 



