868 ANATOMY AND PATHOLOGY 
Table VII. — Grain count data of A-8 grain category'^ 
Stock 
Cholesterol 
Days after 
^H-thymidine 
administration 
Labeled cells 
c 4-8 grains/ 
total c > 4 
grains 
% 
Av % 
for 
group 
Labeled cells 
c 4-8 grains/ 
total c > 4 
grains 
% 
Av % 
for 
group 
p value** 
2 
204/1022 
212/981 
20.0 
21.6 
20.8 
311/1077 
430/1156 
28.9 
37.2 
33.1 
— 
7 
327/1017 
32.2 
394/1002 
39.3 
358/1043 
34.3 
33.2 
293/727 
41.1 
42.3 
.06 
340/1031 
33.0 
314/674 
46.6 
lO 
1 f\(\ /Q9Q 
oi.U 
9/4 Q /KC9 
44.1 
1 1 7 /jll Q 
llo/ 410 
97 i 
oil/ 04 1 
00. 1 
04.4 
■Uo 
118/288 
41.0 
306/506 
60.5 
30 
215/522 
359/722 
41.2 
49.7 
418/539 
718/973 
77.6 
73.8 
354/905 
39.1 
44.7 
622/1008 
61.7 
68.8 
.001 
100/227 
44.1 
144/225 
64.0 
106/193 
54.9 
241/357 
67.5 
35/90 
38.9 
173/253 
68.4 
♦ Percentage of labeled cells with 4-8 
1 grains among 
total labeled 
cells with > 4 grains. 
** Mann- Whitney U test. 
Table VIII. — Labeling indices* of i-8 grain category from grain count data 
Stock Cholesterol 
Days after 
^H-thymidine 
administration 
Labeled cells c 
4-8 grains/ 
total cells 
9f 
Av % 
for 
group 
Labeled cells c 
4-8 grains/ 
total cells 
% 
Av % 
for 
group 
p value* • 
2 
204/23,750 
0.87 
1.00 
311/52,810 
0.59 
1.14 
212/18,790 
1.13 
430/25,570 
1.68 
7 
327/28,750 
1.14 
394/23,920 
1.65 
358/30,140 
1.19 
1.15 
299/26,710 
1.12 
1.46 
Not sig- 
340/29.440 
314/19,440 
1.62 
nificant 
16 
100/15.170 
0.66 
248/29.250 
0.85 
113/23.920 
0.47 
0.66 
321/29,720 
1.08 
1.08 
.06 
118/14,020 
0.84 
306/23,300 
1.31 
30 
215/17,100 
1.26 
418/13,050 
3.20 
359/16,930 
2.12 
718/20,670 
3.47 
.032 
354/18.420 
1.92 
1.05 
622/26,062 
2.39 
2.35 
100/13.680 
0.73 
144/22,200 
0.65 
106/46,710 
0.23 
241/9,110 
2.65 
35/54,160 
0.06 
173/9,930 
1.74 
* Percentage of labeled 
cells with 4-8 grains 
among 
total cells, labeled or 
unlabeled. 
*• Mann- Whitney U test 
the cycle) from Gi or Go cells in the cholesterol 
group than in the stock group. This means that 
the time in Gi or Go has been shortened. 
The results of these experiments permit us to 
define at least in broad terms some of the ele- 
ments of the cell cycle shown in Figure 1. We 
know from the labeled mitoses experiment that 
the duration S + Go + M is less than 37 hours. 
We cannot estimate S in the usual manner^" 
from the labeled mitosis curves because of the 
5-hour spread produced by colchicine. However, 
we can say that S is no more than 15 hours and 
probably less (preliminary results from a study 
in progress suggest an 8-10 hour S). Go is at 
least 7 hours, for the first labeled mitoses were 
seen in the swine given colchicine 7 hours after 
receiving ^H-thymidine and sacrificed at 12 
hours. There is no reason to believe that M is 
any longer than 1 or 2 hours. No evidence is 
presented indicating that any of these times dif- 
fer significantly between the cholesterol swine 
and the stock swine. 
The division observed during the first 2 days 
represents the completion of a partial genera- 
tion, beginning with S. No evidence for a sec- 
ond division is apparent up to 30 days. Hence, 
the generation time of SMC in both controls 
and cholesterol animals must exceed 28 days. 
Thus the extent that the generation time of the 
cholesterol group has been decreased by choles- 
