MITOSIS IN CENTRAL NERVOUS SYSTEM , 557 
TABLE 2 
Showing the number of mitoses per cubic millimeter of nerve tissue in the central 
nervous system at certain levels. The figures are taken from calculations of the 
volume of tissue and the number of mitoses in ten consecutive sections at each level of 
the cord, five in the largest portion of the cerebellum and five in the cerebrum in the 
region of the optic chiasma (see p. 652). The numbers italicized are from the same in- 
dividual of that age. Theletters (a), (b) and (c) refer to different rats of the same age. 
| CORD 
CEREBELLUM | CEREBRUM 
AGE es aT = 7 = 
Cervical Thoracic Lumbar 
days 
1 208 || 115 259 1597 | 430 
4 Lo ater gre ao) CT | Ditiple |. eeey, 
6 | 46 | 236 | 320 (7-day)4848 | 193 
12 46 15 eae | 839 | BT, 
20 00 =| OOn | 00 | (a) 00! (a) 18 
20 | 00 | 00 OOM =) NEY RG NG) 27 
20 | OO. | 00 00 Cf (c) 520 | 
25 | 00 | 00 | 00 00 a7 
The differences of quantitative distribution which appear from 
this table if one reads the figures from left to right (accord- 
ing to the same age) have been noted on page 555. If one reads 
the columns downwards, it appears that the rate of cell division 
increases after birth (a confirmation of Hamilton ’01) until the 
sixth day in the cord and the seventh in the cerebellum, but in the 
cerebrum only until the fourth day; after these respective dates 
the rate decreases rapidly. Cell division has ceased in the cord 
at the twentieth day, in the cerebellum at the twenty-fifth day, 
but in the cerebruin is still continuing at this last age at the same 
rate as for the twentieth day in specimen 6. 
Since these figures are taken from so limited a number of 
animals of each age, and from a length of only 80 micra in the 
cord and 40 micra in the brain at each level, they are to be inter- 
preted as representing the general movement of mitotic activity, 
not as furnishing the basis for an accurate curve which will show 
the rate of mitosis after birth. More data must be gathered 
before such a curve can be constructed. However, the wide 
difference at each age between the rate in the cerebellum and the 
other levels indicates that we are safe in concluding that this 
organ presents the greatest degree of activity. There is good 
