40 A. T. RASMUSSEN 



the veins before the fixer was injected, as is done regularly by 

 Cowdry. These three control animals are at the bottom of each 

 group in the accompanying table of results. Further treatment 

 was done according to the outline given by E. V. Cowdry ('16 b). 

 Sections were cut 2/x thick except in the case of the spinal cord 

 where the sections were cut S/x. Such thin sections were neces- 

 sary to facilitate and make more accurate the counting of 

 mitochondria. 



At least four consecutive sections from a given block were 

 mounted on each of ten or more slides and stained with a 20 per 

 cent solution of acid fuchsin in aniline water and differentiated 

 with a 1 per cent aq. sol. of methylgreen after various degrees 

 of dechromation. Several slides were made under what appeared 

 to be the optimum conditions so as to insure plenty of well- 

 differentiated sections. By having four or more consecutive 

 sections mounted on each slide it is possible to rule out any varia- 

 tion in thickness which might escape general inspection by count- 

 ing the mitochondria in an equal number of cells from each of the 

 four (or a larger even number) consecutive sections and using the 

 average. As a matter of fact, only in a few cases was there any 

 trouble in getting uniform cutting, despite the extreme hardness 

 resulting from long fixation and the high melting point (60° to 

 62°C.) of the paraffin. A difference in thickness in sections cut 

 as thin as 2yu is readily noticed by the much greater tendency of 

 the thinner ones to wrinkle, so that only such regions of the rib- 

 bon as showed uniformity in cutting were used. 



In selecting the levels for study important nuclei and ganglia 

 in which the cells have a more or less well-known function were 

 selected, as is seen in the accompanying table of results and re- 

 lated data. In the case of the spinal cord the sixth cervical seg- 

 ment was used for somatic motor cells of the ventral cornu and 

 the seventh thoracic segment for visceral motor cells of the lateral 

 cornu. The seventh thoracic and sixth cervical spinal ganglia 

 were used for dorsal root ganglion cells. In the cerebellum the 

 cortex from the inferior portion of the vermis was utilized. No 

 comment is necessary on the other regions selected. It is be- 

 lieved that sufficiently varied types of cells have been chosen to 



