MITOCHONDRIA IN NERVE CELLS 41 



be a fair index to the mitochondrial behavior in the nervous sys- 

 tem under the conditions of hibernation and to rule out the ob- 

 jections frequently made to conclusions drawn from alterations 

 detected in only a single type of cells (usually the Purkinje cells 

 of the cerebellum) which often are apparently only remotely 

 related to the physiological process under investigation. 



In determining the number of mitochondria a Whipple eye- 

 piece micrometer disc (Bausch & Lomb), on which squares of 

 various sizes are ruled, was used. In general the medium-sized 

 square (r 00 of the entire ruled field) was used as the unit. This 

 area with the oil-immersion objective, ocular, tube length, etc., 

 used and which were, of course, kept constant throughout the 

 determinations, gave a field of jpn sq. mm. In the case of 

 sections 2\i thick the cubic volume represented by each square 

 is 6,805,5oo cu - mm - I n order to reduce all figures to the number 

 of mitochondria in million per cu. mm. of cytoplasm the num- 

 ber of mitochondria found in the above small volume was mul- 

 tiplied by the factor 6.8. The corresponding factor for sections 

 Sfj. thick is 4.537. All figures given, therefore, indicate millions 

 per cu. mm. of cytoplasm. For each type of cell in each animal 

 the average of at least twenty fields from twenty different cells 

 is given. Since there are five animals in each stage, the figure 

 for each stage as a whole is the average of 100 cells. 



As a preliminary study, the total number of mitochondria in 

 such sections of cells as contained the nucleolus were counted. 

 On account of the irregularity in shape and the great personal 

 factor necessarily involved in deciding on what shall be consid- 

 ered the limits of the cell body, these figures are not given. They 

 showed, however, exactly the same results as obtained by the 

 quantitative determinations. Obviously, the results stated in 

 terms of the number in a known volume of cytoplasm are the 

 only facts capable of comparison with the work of other investi- 

 gators. Due to the difficulty experienced, under the best optical 

 conditions available, in determining the number of mitochondria 

 when too closely packed, as they are occasionally in small clumps, 

 the figures are necessarily only approximate; but they are be- 

 lieved to be sufficiently accurate for comparative purposes. 



