866 
ANATOMY AND PATHOLOGY 
of the labeled cells, since a second division 
would not have resulted in most cells having 
less than 9 grains. Hence, the results of the la- 
beled-mitoses experiment was consistent with 
no more than one division in 47 hours for both 
stock and cholesterol diet-fed swine. The gener- 
ation time cannot be ascertained from this 
study, since it would be necessary to follow the 
labeled cells through two divisions. 
The approach chosen in order to estimate the 
generation time was to pulse-label the cells with 
^H-thymidine and follow the grain count distri- 
bution of the labeled cells at different periods of 
time. Thirty-eight swine were given ^H-thymi- 
dine at day 0. Two hours later, 8 swine were 
killed to provide the baseline grain count distri- 
bution, that is, the grain counts after the pulse 
labeling was completed but before the labeled 
cells had divided. The remaining swine were di- 
vided into two groups and fed either the stock 
or cholesterol diet. The swine were killed in 
pairs at 2 days, 7 days, 15 days, and 30 days. 
The tissue studied was cross-sections of the aor- 
tic trifurcation of the abdominal aorta. The 
specimens were processed for autoradiography 
and grain counts of labeled cells were made. 
From the baseline grain count, a generation 
table such as that shown in Table V can be con- 
structed. The numbers on this table are pre- 
sented only as stylized illustrations and bear no 
relation to the actual experiment. The Co col- 
umn represents the number of cells in the corre- 
sponding grain category listed in the first col- 
umn. 
When these cells divide, each daughter cell 
will have half as much ^H-thymidine as the 
parent,^^ and at least in a statistical sense will 
produce half as many grains under standard- 
ized conditions. By utilizing this fact, the num- 
ber of potential parents for each grain class in 
the next generation can be determined. For ex- 
ample, all of the cells with 16 grains are poten- 
tial parents of cells with 8 grains. 
However, these are not the only potential 
parents for cells with 8 grains, since cells in the 
original population with odd numbers of grains 
must also be accounted for ; and these must be 
handled in a special way. For example, we can 
assume that in a statistical sense half of the 
cells with 15 grains at the outset will be parents 
of daughters with 8 grains and half of daugh- 
ters with 7 grains. Likewise, half of the cells 
with 17 grains can be considered as potential 
parents of cells with 8 grains and half of cells 
with 9 grains. Thus the total available parents 
for cells with 8 grains will be all in the predivi- 
sion population with 16 grains plus half of 
those with 15 and 17 grains, respectively. 
The above process can be repeated with each 
grain class until the number of potential par- 
ents for each class in the next generation has 
been determined. This process can be used to 
construct a generation table for any number of 
generations that are desired. 
Table V. — Examples of construction of a generation table using cells observed after pulsing with -thymidine but 
before division 
No. of grains 
Co" 
No. of cells in each 
grain class after pulsing 
but before division 
Cells in C„ reclassified 
as potential parents 
Cells in C^ reclassified 
as potential parents 
0-3 
40 
168 
4 
10 (5.0%) 
40 (25.0%) 
32 (100%) 
6 
10 (5.0) 
40 (25.0) 
6 
10 (5.0) 
35 (21.9) 
7 
20 (10.0) 
20 (12.5) 
8 
20 (10.0) 
20 (12.5) 
9 
20 (10.0) 
5 (3.1) 
10 
20 (10.0) 
11 
20 (10.0) 
12 
20 (10.0) 
13 
10 (5.0) 
14 
10 (5.0) 
IS 
10 (5.0) 
16 
10 (5.0) 
17 
10 (5.0) 
Total > 4 
200 (100%) 
160 (100%) 
32 (100%) 
