7 
1906-7.] Effect of Meat Diet on Fertility and Lactation. 
np to the end of the experiment. This reservation must, however, be made, 
that one of these 9 animals probably had young which were eaten, and it 
is just possible that this happened in other cases. It is not at all probable, 
however, as the animals were frequently carefully examined, and if there 
was any indication of their being pregnant, were at once transferred to 
separate cages. 
Of the 12 animals fed on a bread-and-milk diet, all became pregnant 
and had young, so that we may conclude that a meat diet is decidedly 
prejudicial to the occurrence of pregnancy in rats when the diet is begun 
when the animals are from 2 to 4 months old. 
In order to determine whether the fault resided in both sexes or in only 
one, a fresh male which had been fed on bread-and-milk was put beside the 
sterile females which had been on meat for several months. When the 
animals were killed, some time after, one of them was found to be in an 
early stage of pregnancy, and must have been impregnated by the bread- 
and-milk male. 
This would appear to indicate that the cause of the sterility is partly 
due to the male, but we have not had sufficient material to form any more 
definite conclusion regarding this. 
2. Effect of a Meat Diet on Lactation . — For this part of the investiga- 
tion the same animals were used, viz., the 12 controls fed on bread-and- 
milk and the 8 meat- fed animals which became pregnant. The point 
specially attended to was the weight of the mammary tissue of the animals 
killed after suckling their young for varying periods. 
In the nursing rat the mammary tissue forms a continuous sheet spread 
under the skin of the abdomen on each side of the middle line. In addition 
there are extensions of it into the axillae, up along the neck and into the 
groins, while in some cases it spreads out so much laterally as almost to 
reach the back. The nipples are in a double row extending from thorax to 
the groins. 
The animals were killed at different periods during lactation. The 
weight of the mother and the number and weight of the young at the time 
of death were ascertained. The skin and subcutaneous tissue of the 
mother’s abdomen was immediately removed down to the muscle, care 
being taken that no mammary tissue was left behind in the axillae or in 
the groins. The skin was put into 5 per cent, formalin for a few days, 
when it was quite easy to separate the mammary tissue from the skin on 
one hand and from the areolar tissue on the other (see fig.). If an attempt 
were made to strip the mammae before first fixing in formalin, it was found 
that a great deal of milk was squeezed out. The immersion in formalin 
