Oct. is, 1924 Postnatal Growth of the Single-Corrib White Leghorn 
369 
the chicks from Groups 2, 3, and 4 is 
below the initial weight on the first, 
second, and third days, with the mini¬ 
mum on the third day. The initial 
weight is that observed when they were 
taken from the incubator. Not until 
the fourth day is the average weight 
greater than the initial weight. This 
decrease takes place although the 
chicks begin picking up sand as soon as 
placed in the brooder. The gizzard of 
the chick autopsied after one day was 
filled with fine sand, and the digestive- 
tract contents formed 4 per cent of the 
net body weight. In the chick at two 
days this tare formed 12.1 per cent, and 
at three days it had risen to 15.8 per 
cent of the net body weight. 
The gross weights of the 100 autop¬ 
sied chickens shown in Figure 1 are higher 
From the foregoing data it may be 
concluded that the chicks show a post¬ 
natal loss in body weight which is not 
recovered until the fourth day. The 
curve of postnatal growth in weight 
shows three general phases: First a 
period,of slow growth, then a period of 
rapid growth, followed by a slow in¬ 
crease which may continue for some 
time. There is possibly a slight 
prepuberal retardation and rise, but 
this is doubtful. After 70 days the 
cockerels become distinctly heavier 
than the pullets of corresponding age. 
GROWTH IN LINEAR MEASUREMENTS 
Body length. —-The growth in 
length of the chick from the tip of the 
beak to the cloacal orifice is shown in 
the chart in Figure 3. The formulas 
Pig. 3—Nose-to-anus length, or body length from tip of bill to cloacal opening, measured in centimeters 
and plotted on age in days. The females (circles) appear relatively shorter after 115 days of age 
than the average live weights for the 
groups from which they came. During 
the earlier part of the work, individuals 
conforming to the average weight as 
given by Card and Kirkpatrick { 2 ) for 
corresponding ages were selected, and 
this naturally raises the average for the 
autopsied chickens. 
The drop in the average weights of 
the pullets after 200 days (fig. 1) is 
similarly due to the removal of the 
larger pullets earlier in the experiment, 
and is not the result of a decrease in 
weight of the individual pullets. The 
weights of the six older birds indicate a 
continued slow average increase in the 
period after the weighings were stopped. 
This increase is due very largely to an 
increase in adipose tissue, although 
some organs continue to grow, as will 
be shown later. 
from which these curves were drawn 
are, for the males from 10 to 145 days: 
Y = 2(X 0 - 58 ) + 0.013X + 6.07; from 
145 to 300 davs, F = 0.0143(X- 
145) +43.79. 
The formulas are, for the females from 
10 to 115 days: 
F=2(X 0 - 58 ) +0.013X+6.07, and 
from 115 to 300 days, Y = 
0.0211(X-115) + 38.89. 
Y represents the body length in cen¬ 
timeters and X represents the age in’ 
days. 
A comparison of this chart and that 
in Figure 1 shows that nearly the maxi¬ 
mum length is reached at about 115 
days for the pullets, or when they reach 
about 55 per cent of the mature weight; 
