1912] Read: Suckling Period in the Guinea-Pig 343 
It is thus observed that the fat-content of the guinea-pig’s 
milk is very high. The reason for this may be explained as 
follows: 
As previously stated, the young guinea-pig is but very slightly 
dependent upon the mother’s milk after the third or fourth day, 
for at this age it begins to eat the same food as the adult. There 
is one food, however, of which it has more need in proportion to 
its size than the adult. This food is fat, which has as its chief 
function the supplying of heat to the body. The loss of heat 
from the body-surface of a small animal is greater in proportion 
than that from the body of an adult, because the proportion of 
surface to volume is greater in a small than a large body (1.e., 
surface increases as the square, and volume as the cube of the 
linear dimension). 
Recognizing this fact then, it is clear that the young guinea- 
pig must get more fat than is contained in the solid food which 
it eats. This same food contains all the fat which the adult 
needs. In fact it seems to contain more than is ordinarily re- 
quired to maintain body temperature, for in no other way can 
the following phenomenon be accounted for. 
Guinea-pigs as well as human beings accumulate a reserve 
store of fat during pregnancy. This is used up during lactation, 
as can be shown by the rapid loss of weight which a nursing 
eulnea-pig undergoes. Table IT (C. 8. Minot, 1891, p. 144) shows 
that on an average 63.8 grams were lost by the animals under 
observation during the normal nursing period. 
TABLE II 
Alterations of weight of female guinea-pigs during lactation 
Days after Number of Average Daily per cent 
delivery observations weight increase 
0 24 GIS:64 ey een 
1-5 55 575.6 — le 
6-10 51 596.2 —0.7 
11-15 36 581.5 0.9 
16-20 36 572.1 —0.3 
21-25 28 549.8 —0.8 
The great loss of weight leads us to believe that the high per- 
centage of fat in the guinea-pig’s milk comes from the fat stored 
up in the tissues during pregnancy. 
