362 MARGARET R. LEWIS AND WARREN H. LEWIS 



This is also true of cells undergoing division, for there seems 

 to be no amount of mitochondria characteristic of any one 

 phase of division. Also the variation in the quantity of mito- 

 chondria present in any one phase of division is considerable, 

 as can be seen (figs. 14, 15, 16). Daughter cells usually have 

 a smaller quantity of mitochondria than the metaphase cell or 

 than the resting cell (fig. 17). 



As to the question whether the amount of mitochondria in- 

 creases during mitosis it is impossible to state. So far, we have 

 only one definite observation that this is true. In this case the 

 living culture was subjected to a temperature of 46 °C. for two 

 hours, during which period the mitochondria decreased decidedly 

 in number and size. Two cells which were under observation 

 suddenly began to pass into prophase and during this process 

 the number of mitochondria in these two cells increased until 

 they contained more than they had before the experiment was 

 begun. Although several subsequent experiments with increased 

 heat caused a decrease in the quantity of mitochondria no cell 

 division was observed. 



No agent but heat has so far been observed which caused a 

 change in the amount of the mitochondria without injury to 

 the cell. However, it is evident that certain metabolic condi- 

 tions must cause a change in the quantity of mitochondria. 



Relation between position, size, number and quantity of 

 mitochondria 



No definite relation between the position, size, number and 

 quantity of the mitochondria has been observed in the cells of 

 the tissue cultures, still there is a more or less marked manner 

 in which the mitochondria occur in the cells. Frequently the 

 long threads or short rods are plentiful and scattered throughout 

 the cytoplasm with or without a definite central body. When 

 the mitochondria are in the form of large granules and thick rods 

 they are fewer in number and are arranged more or less radially 

 around a central body. When only a very few mitochondrial 

 granules are present they are usually of the large granule type. 



