GROWING TEETH IN A RAT'S HIND LEG

Evening Post, Volume CXXII, Issue 106, 31 October 1936, Page 27

GROWING TEETH IN A RAT'S HIND LEG

■Experiments in which the undeveloped teeth of a ,rat embryo were transplanted and made to- grow in the hind leg of the mother animal, were described recently before the tercentenary session of the Harvard Dental School and the Harvard Dental Alumni Association, says the ■ "New York Times." ■

The experiments,, it was made clear, were not carried out with a view of creating an., animal that could kick and bite at the same time. Nor were they meant to be taken as foreshadowing an era of "teething rings for grandmothers" by carrying the experiments to the stage of transplanting the mandibles "of prematurely born humans intoadults.' ■

The intention of the experiments, it was pointedout by Dr. Lawrence W. Baker, who made the report, was to find out the influences which cause the growth of bones".' r "I have found," Dr. Baker reported, "that there are two sets of influences which cause bone to grow, and which enable the bones of the face and head to develop.

"One set is pre-natal. It is inherent in the bone in the germ plasm. Th 6 other set is post-natal and is functional ' ' ■ . • "Through successful transplants, we are able to separate these two great growth influences and thus study these forces in isolation."

"I have believed that by transplant-, ing teeth and their supporting structures while in their embryonic state," Dr. Baker continued, "we could study the growth of. these parts in a new environment and. in isolation. Thus further knowledge might be gained not only about these structures but about the influences of their growth forces upon the development of ;the bones of the face and internal bony structure of the- head.

."As a result valuable information could be placed at the disposal of all who work upon this important part of the human body, the head."

The "sites" selected for transplanta-tion-of the embryo mandibles have been the eye, leg muscles, and the

brain, Dr. Baker said, and continued:—

"We succeeded in obtaining 'takes' in all three structures. It was found, however, that the best results 'were obtained in muscle, probably because of the fact that the transplanted bone was in, its most normal, environment, functioning striated muscle." ... . .

Dr. Baker and his associates: trans-. planted half of an embryonic rat man-, dible, taken three days before birth, and. compared it with the other untransplanted half of the same mandible forty days after' the transplant. The transplanted half had grown considerably t while the non4ransplanted half ■remained the same. :

In this way the pre-natal growth factor could bedetermined. The growth of • the transplanted half of the mandible was then compared with -the growth of a normal mandible after forty days. The growth was larger in size but the-shape-in both cases was the same. . •■

In this manner the post-natal growth factor was separated from the pre-natal factor. ;

"Evidently," Dr. Baker stated; "the inherent, pre-natal developmental forces are very strong, for the body of the transplant, with its complex forms, have all taken definite shape. "That so much of the architectural plan of this complex bone, which develops from multiple centres of ossification and which contains the intricate and constantly growing . dental apparatus, appears to be determined within the, germ plasm, is indeed remarkable." The transplant of the. mandible into the brain, Dr. Baker added, throws some light on vthe reason why infections of the brain are relatively rare.

The reason was attribued to the existence'of a certain barrier in the blood vessels.of the train,.particularly the capillaries, which Resist the ingress of infectious to the. .brain, ;,

The observations on the results, of the transplant of bone into the brain, Dr. Baker stated, "would seem to. indicate that there may be something, else in the tissues of the brain besides the capillaries which resists infectious bacteria."