Hardesty, Medulla Spinalis of the Elephant. 163 



results more nearly expressive of the relations sought. In col- 

 umn 5 of Table III the total areas are given of each of the 

 transverse sections exclusive of the pia mater. To obtain these 

 areas each section was first enlarged to reduce the error, and 

 an outline tracing made of the projected image. The area of 

 this tracing was then taken with the "Kugelrollplanimeter" 

 (invented by G. Coradi) and the result divided by the square 

 of the number of diameters by which the original had been 

 enlarged. The planimeter used is recommended for its accu- 

 racy and enables one to obtain the area of a figure however 

 irregular its outline. The machine automatically registers an 

 amount from which the area of the figure can be computed to 

 thousandths of a square mm. To insure no mistake and to 

 minimize the possible error, each tracing was gone over with the 

 planimeter three times. The areas recorded in columns 6 and 7 

 were obtained in a similar way. 



Using the areas of the sections instead of their diameters 

 in the comparisons, it will be found that the elephant having a 

 body weight 6 times that of the horse has a medulla spinalis, 

 the transverse section of which in the cervical region has an 

 area but little more than 2 times that of the horse. Or, having 

 a body weight at least 50 times that of man, the elephant has 

 has an area of section only about 3 times of man. Conserva- 

 tively speaking, the elephant is 180,000 times as heavy as the 

 white mouse, but the area of the section of its cervical medulla 

 spinalis is only 156 times that of the mouse. These results are 

 somewhat higher than those obtained from comparing the diam- 

 eters of the specimen. 



If similar comparisons are applied to the other members 

 of the series, results will be obtained gradually varying from 

 the larger mammal to the smaller. 



The general statement that the smaller the mammal the 

 greater is its central nervous system in proportion to the size of 

 the body, may be emphasized by making another comparison 

 between the elephant and the mouse. If the size of the mouse 

 is increased to the size of the elephant and at the same time 

 the prop'ortion maintained between the area of the section of 



