372 MARGARET R. LEWIS AND WARREN H. LEWIS 



mitochondria during mitosis. So far we have only one direct 

 experimental observation to offer, and in this particular case 

 there was an actual increase in the number and possibly also 

 in the quantity. In this experiment the temperature had been 

 raised from 39 to 46°C. and was retained at 46°C. for two hours. 

 There resulted a decided decrease in the amount of mitochondria 

 within all the cells. Two cells began to divide. The nuclear 

 wall disappeared, the nucleoli faded and the chromosomes ap- 

 peared. These cells, which a few minutes before had contained 

 only a very few mitochondria, now became full of short dumb- 

 bell-shaped rods, while the resting cells did not undergo any 

 change. So far as could be seen by most careful observation, 

 this increase in quantity of mitochondria was not due to the 

 division of the existing granules. 



Mitochondria in different kinds of cells 



Regardless of the fact that the mitochondria constantly change 

 in shape, size and quantity in any one cell, there is a character- 

 istic appearance of the mitochondria in certain kinds of cells, 

 as, for instance, the short, rod and dumbbell shapes are most 

 frequently found in the cells of the endodermal membrane; 

 the long threads, rods and sometimes loops are found more fre- 

 quently in the connective tissue; the small granules and short 

 rods are frequent in nerve fibers and cells, and are often much 

 smaller than those of the connective tissue cells over which the 

 nerve fiber passes; a striated arrangement together with scat- 

 tered granules is characteristic of the fibroblasts; and the large 

 granules are more frequently seen in the heart and smooth 

 muscle syncitium than in any other kind of tissue. At times 

 the growth from the explanted intestine or heart contains only 

 cells with thread- and rod-shaped mitochondria. Again, a large 

 proportion of such cells contain only large granules. These 

 granules are frequently so large that they are clearly seen with 

 the low power. They are collected about the central body and 

 appear to be more refractive than other types of mitochondria. 

 Occasionally these large granules fuse. That they are not a 



