The clinical results obtained in an experimental investigation on the influence of an excessive meat diet on the growth and nutrition of rats are described on p. 565. It was there shown that the progeny of meat-fed rats are usually poorly developed, and show a high mortality in early life. The present chapter comprises an account of the naked-eye and microscopic appearances observed in the osseous system of these meat-fed subjects. The material employed consisted in the young of mothers fed for some weeks or months prior to pregnancy, and during pregnancy and lactation, on a diet of ox-flesh, the animals, after weaning, being continued on the meat regime, an equal number of controls being taken from the young of rats fed on an exclusively bread and skim milk diet. Doth diets were given in unrestricted amount, and with the meat diet water was given ad libitum. Over a hundred meat-fed rats were utilised for the investigations, their ages ranging from one day to three months, the majority being under three weeks old at the time of death. A record was made of the naked-eye appearances of the skeleton, special attention being directed to the consistence as well as to the general appearance of the long bones, ribs, and flat bones. The tissues were fixed in formalin (5 per cent), decalcified in weak nitric acid solution, and stained in the ordinary manner with hematoxylin and eosin. Sections were made through the anterior part of the cranium so as to demonstrate the conditions present in the frontal, malar, and maxillary bones, while, in the case of rats art. one day, three weeks, and two months respectively, sections were also made of the tibia, humerus, and ribs. Similarly prepared sections from control animals were, for comparison, mounted on the same slide.

Macroscopic Appearances

The macroscopic conditions noted in the bones of the meat-fed rats very according to the age of the animals, but show throughout, in a more or less marked degree, the same general characteristics. The most striking feature is the marked general softness of the whole osseous system, this condition being present in every meat-fed subject. The long bones of the flesh-fed rats are distinctly softer and more pliable than those of the bread-and-milk-fed animals; a similar condition is observed in the ribs, short bones, and cranial bones of the meat-fed rats. This soft condition is present in the bones at birth, and becomes accentuated as age advances. A second striking appearance in the meat-fed animals is the darker colour of the long bones, more especially of the ribs, this being due to increased vascularity. This condition is present, in a greater or less degree, in all the meat-fed subjects which died or were killed after the second week of life. In some cases nothing further was observed in the bones of the flesh-fed rats killed even as late as three months after birth, but in the majority of cases a third feature shows itself. During the second month various curvatures of the spine and long bones occur. These consist in marked scoliosis and lordosis, with bending of the ribs at their angles, while curving of the bones of the limbs is present in a less degree. This condition of the bones is usually associated with an enlargement of the costo-chondral junction. In a small percentage of cases (about 15 per cent.) an additional feature is the presence of small white nodules in the bony ribs, these nodules standing out as pale bead-like prominences in the substance of the dark bone of the rib. On section these nodules are composed chiefly of cartilage (see Fig. 18). In the more pronounced cases the skeletal changes generally are similar to those seen in advanced cases of rickets in the human subject. Microscopically, however, this similarity is not borne out.

1 Chalmers Watson, Lancet vol. ii., 1906.

From a vertical section of the Cranium of a Rat set. three months, fed on ox flesh.

Fig. 12. - From a vertical section of the Cranium of a Rat set. three months, fed on ox-flesh.

Note the imperfect development of the frontal bone and the increase in the size of the medullary cavity. The mucous membrane of the nose is in a state of catarrh. Cf. Fig. 13.

From a vertical section of the Cranium of a Rat set.

Fig. 13. - From a vertical section of the Cranium of a Rat set. three months, fed on bread and milk.

Note the well-developed frontal bone.

[Face page 590.

From a vertical section of the Cranium of a Rat set.

Fig. 14. - From a vertical section of the Cranium of a Rat set. three weeks, unwearied. Mother fed on an ox-flesh diet. For comparison with Fig. 15. (x 75).

Note the imperfect development of the frontal bone and increase in the size of the medullary cavity.

From a vertical section of the Cranium of a Rat aet.

Fig. 15. - From a vertical section of the Cranium of a Rat aet. three weeks, unweaned. Mother fed on a hread-and-milk diet. The photograph shows the frontal bone, and the upper part of the nasal septum and nasal cavities, (x 75).

Note the normal state of development of the frontal bone. Cf. Fig. 14.