Since 1889 when Brown-Séquard, at the age of 72 (6 years before his death) put forward the idea that rejuvenation could be brought about by the hypodermic injection of testicular emulsion, the view that old age and senile changes are due to failure of the glands of internal secretion has become popular. The thyroid (V. Horsley, Léopold-Lévi), the testis and ovary, or most or all of the glands (pluriglandular insufficiency) have been incriminated; Lorand,[94] indeed, regards old age as a disease caused by degeneration of not one but several of the endocrine glands, Biedl[95] expresses much the same view in referring old age to a disturbance of the endocrine balance, and Berman[96] in a recent semi-popular book states that old age is an exhaustion permanent and irreparable of all the glands of internal secretion; like Lorand he ascribes considerable importance to failure of the internal secretions of the sexual glands. It is highly desirable to arrive at some conclusion as to the relation between changes in the glands of internal secretion and senescence, for in medical practice this conception of cause and effect has been acted upon; various glandular extracts have been employed to counteract and delay the disabilities that may accompany advancing years and, though not so freely, operations, viz., ligature of the vas deferens and implantation of testicular grafts, have been carried out. Lydston[97] implanted testes from boys recently dead into men with atrophied or destroyed testes and reported improvement. Stanley and Kelker[98] implanted 11 cases with testicular grafts obtained from executed criminals, and 5 cases with the testes of rams, obtaining improved general condition, though not claiming that life was prolonged. Stanley[99] injected by means of a large syringe strips of testes of rams, goats, or bears under the skin of the abdomen of more than 300 prisoners, and stated that conditions of neurasthenia and senility were relieved.