A much more reasonable and probably true explanation of the cause of old age is the gradual disappearance of animal matter in the bones and tissues, and the corresponding increase of the mineral matter in the bones and tissues, amounting to ossification of cartilage, whereby the supple cartilage, losing its animal content, becomes practically bone by deposit of lime particles. This would also account in a common-sense manner for the fragility of the bones of the aged, the brittleness being due to calcareous deposits in the substance of the bone itself, in excess of the normal mineral contents of the bones in youth. The function of the seminal fluids, therefore, appears to be to restore to the aging tissues this property, this animal matter, which when in its right ratio and proportion in the cells of the organism produces the condition of youth. The action of these seminal fluids, therefore, seems to be two-fold, a dissolving and a nourishing. The distinction should be clearly made that the action is NOT merely stimulating. The stimulation of a nerve-cell is a temporary excitement. We speak of the stimulation of alcohol, and this illustration gives a clearer view of the difference between the nourishing action of the seminal fluids and a stimulating action than we could obtain by the employment of many words. It is interesting to remember that while it is possible to increase the mineral particles of soda, potash, lime, iron, silica and magnesia in the blood and lymph, it is practically impossible for us to increase the animal contents of the cells by any method of medication or dieting known to us. Only Life can produce this change in the cells, and only this method of gland-transplantation has furnished a means of impressing Life into service to work for us in this matter. To produce the effects which are needed to rejuvenate a body that has increased its mineral matter at the expense of its animal matter we require the co-operation of glands made active, because only the glands, in the marvelous chemistry of the body, are able to compound the animal substances required to nourish the cells, tissues and organs of the body, and to dissolve and remove those injurious substances of a mineral nature which have accumulated in excess in cells and tissues, usurping the place of the animal matter in the cells because of the inactivity of function generally, and the poor elimination of waste matter, as the years pass. This is the re-creative and rejuvenating work of the gland secretions. It is beyond us to say exactly what these secretions consist of. We know the importance of their presence in blood and lymph only by the disasters that follow their absence. The thyroid gland and parathyroids, for instance, seem to be connected by some close sympathy with the activity or non-activity of the interstitial glands, and the atrophy of one is often accompanied by the atrophy of the other. The subject is