In view of the results obtained from an investigation on the influence of 1 raw-meat diet on the thyroid and parathyroid glands in fowls, it was deemed advisable to repeat the investigation with other animals, e.g, rats. Twelve animals were used for this experiment, with eight controls. Eleven of these were young subjects, their ages at the outset of the observations ranging from six to twelve weeks; the twelfth was a full-grown rat of unknown age. Except in the case of the adult rat, the control subjects were taken from the same litter as the animals placed on special diet. This diet consisted of raw minced ox-meat and water, as much meat being given as the animals would consume; the diet of the control cases consisted of bread and milk and occasionally porridge, also in unrestricted amount. The investigations lasted in some cases six weeks, in others four months. The results may be summarised.

Clinical

For the first ten days or so all the rats on meat diet either lost weight or failed to increase in weight like the control subjects. Subsequently six of the meat-fed animals put on weight to an amount almost equal to that of the control subjects; in the remaining six animals the final record was considerably short of the figures for the bread-and-milk-fed rats. E.g. in one experiment which lasted six weeks, the three animals on the meat diet gained 14 grammes, 15 grammes, and 41 grammes respectively, as against 62 grammes in the case of the control. All the animals appeared in good health, with the exception of the adult rat, which lost weight markedly and died in three weeks.

Thyroid Gland

Macroscopic changes. In three cases there was a distinct increase in the size and weight of the glands, the glands in two instances weighing just double the weight of the control. In the adult meat-fed rat the gland was distinctly diminished in size. In the remaining eight the general appearance of the glands was normal except in one case, in which the parathyroid glands were double the size of any of the control glands.

Microscopic Changes

In ten out of the twelve animals definite histological changes were present, these consisting of: (1) Active proliferation of the epithelium of the vesicles. (2) Congestion of bloodvessels. (3) Mucoid degeneration of the colloid material and of the epithelial cells. In some cases there was also distinct enlargement of the vesicles. The colloid material was diminished in amount. In the adult meat-fed rat the colloid substance had practically disappeared, the general appearance of the gland being one of pronounced atrophic catarrh. The histological changes were most pronounced in the animals which had failed to increase in weight like the control subjects.

Parathyroid Glands

In one out of the twelve animals the parathyroid glands were obviously enlarged, and the microscopical appearances of this gland were abnormal, the epithelial cells being widely separated by large clear spaces, which were apparently areas of mucoid degeneration. A much less degree of the same change was observed in one of the control glands. The parathyroid glands of the meat-fed adult rat were lost in the process of preparation. In the remaining ten cases the histological appearances were normal.

1 Chalmers Watson, Journal of Physiology, vol. xxxii., 1904.

Great hypertrophy of thyroid and parathyroid glands after prolonged feeding on raw meat.

- Prarathyroid.

- Thyroid.

Fig. 4. - Great hypertrophy of thyroid and parathyroid glands after prolonged feeding on raw meat. Weight of one parathyroid gland (Nos. III. and VI.) was 095 and .10 gramme. Weight of one thyroid gland (Nos. III. and VI.) was 1.25 and 1.15 grammes. The average weight of a normal thyroid is .14 gramme.

Transverse section of normal femur at the same level -

To show the changes in the osseous system after fourteen months' raw meat   five sections.

Fig. 5. - To show the changes in the osseous system after fourteen months' raw meat - five sections.

Observe

i. The increase in thickness of the bone. ii. The diminution and obliteration of the marrow cavity, due to the formation of an osteoid tissue, see p. 562.

Fact page 564.

Transverse section of the normal bone seen in Fig. 5, for comparison with Fig. 7.

Fig. 6. -Transverse section of the normal bone seen in Fig. 5, for comparison with Fig. 7.

Transverse section of the abnormal bone in Fig. 5 Same magnification as in Fig. 6. Unstained.

Fig. 7. - Transverse section of the abnormal bone in Fig. 5 Same magnification as in Fig. 6. Unstained.

The general results may be summarised as follow: -

1. The administration of a meat diet to young rats is followed by distinct histological changes in the thyroid gland; this result, although very frequent, is not however a constant one.

2. The changes in the glands are most pronounced in the case of those animals which do not gain in weight at the same rate as the normal animal.

3. The parathyroid glands were in the great majority of cases unaffected by the diet.

4. In the case of an adult meat-fed rat, the animal succumbed after three weeks of the diet, the general appearance of the thyroid gland indicating exhaustion of its functions.