It will be seen that the average percentage weight of the mammae of all the bread-and-milk animals is 9.6, while that of the meat-fed ones is only 8.2. This difference would in all probability have been greater but for the fact that the average number of young suckled by the bread-and-milk animals was only 4.6, while that of the meat-fed animals was 6.3.

As before stated, the longest period before the birth of the young during which the mother had been on a meat diet was thirty days. Taking this into consideration, the difference is sufficiently marked to point to the conclusion that the result of a meat diet is to diminish the amount of mammary tissue in nursing mothers.

Table Giving The Lactation Histoiy Of Twelve Rats Fed On An Exclusive Bread-And-Milk Dietary

Weight of

Animal at Death.

Weight of Mammse.

Per cent.

Time during

Lactation when Killed.

Number at

Young.

Weight of Young.

Grins.

Grms.

Grms.

147

12.5

8

1st day

7

32

140

10

7.1

3rd day

7

45

180

18

10

6th day

7

70

225

18.5

8.2

10th day

7

115

120

17

14.1

21st day

5

150

I40

19

13.5

21st day

7

220

115

7.5

6.5

21st day

3

120

130

11.5

8.8

22nd day

4

100

160

19

11.2

25th day

7

145

160

15

9.3

30th day

6

175

130

13

10

6

...

150

13.5

9

27th day

...

...

Average percentage = 9.6.

The effect of this relatively poor mammary development on the young of the meat-fed rats is shown by a comparison of their weights with those of the young of the control animals towards the end of the lactation period. Thus the average weight of each of the young of the meat rats at the twentieth to the twenty-first day is 21.6 grms., in contrast to 29.4 grms., the average weight of each of the bread-and-milk young. It is thus evident that the young of the animals fed on meat suffer in general nutrition and growth, as compared with those whose mothers are on a bread-and-milk diet.

Whether this is due to a mere deficiency in the amount of milk available for their use, or to some alteration in its constituents, has not been determined, but the probability is that the former plays a large part.

On microscopic examination there are no marked differences in the histological characters of the nummary tissues. The character of the glandular tissue varies according as the acini are full of secretion or empty, and while the mammas of the meat-fed animals show a preponderance of closely-packed empty lobules, this may only be due to the fact that the mothers had been killed shortly after the gland had been emptied by suckling.

Conclusions

1. That a meat diet is prejudicial to the occurrence of pregnancy in rats.

2. That in rats fed on a meat diet the mammary development of nursing mothers is less than in rats fed on bread and milk.