Feeding of thymus to some of the lower creatures of the animal kingdom will completely hold up differentiation.  Take the unfolding of the specialized tissues and organs which transform the tadpole into the frog and the chrysalis into the butterfly.  A tadpole kept supplied with enough thymus in a nutrient medium will swell into an extraordinary giant tadpole, but will not change into a frog.  Recently, this experiment has been contradicted.  Yet this effect corresponds to the conception of its importance in childhood as a retardant of precocity, physical and mental.  Clinical observations emphasize that in childhood it is the chief brake upon the other glands of internal secretion which would hasten development and differentiation, checking them perhaps for a given time and so profoundly influencing growth.

THE PINEAL

The pineal is another gland which has been credited with similar abilities and a like holding-the-reins-tight-in-childhood function among the cells.  Like the thymus, it has been supposed one of the distinctive organs of childhood and to die with it.  Generations of anatomists solemnly asserted, repeating each other’s mistakes with the aplomb of the historians who declare that history repeats itself, that the pineal body was a useless, wastefully space consuming vestige of a once important structure.  That was the view in that century of grandly inaccurate assertions, the nineteenth.  Not that they relegated it with that statement to the limbo of the dull and the uninteresting.  Quite the contrary.  They conferred upon it a distinguished romance and mystery by identifying it as the last heir and vestigial remnant of a third eye, situated in the back of the head, which may still be observed in certain reptiles.  Imagine it!  Somewhere, stuck away in a cranny of the floor of your head and mine, is this descendant of an organ that once sparkled and shone, wept and glared, took in the stars and hawks and eagles, and now is condemned to eternal darkness and an ineffectual sandiness.  Today, we have not discarded that view of its history, but we know a little more regarding its composition and function.

What and where is the romantic object?  It is a cone-shaped bit of tissue hidden away at the base of the brain in a tiny cave behind and above its larger colleague, the pituitary.  Microscopic scrutiny reveals that it is made up in part of nerve cells containing a pigment similar to that present in the cells of the retina, thus clinching the argument for its ancient function as an eye.  But the outstanding and specifically glandular cells are large secreting affairs, which too reach back to the tidewater days of our vertebrate ancestors, when Eurypterus and other Crustaceans were engrossed with the fundamental problems of brain versus belly.  Besides these, there are the singular masses upon which has been fastened the unnecessarily opprobious epithet of brain sand.  These, noted and commented upon from the earliest times, consist of collections of crystals of lime salts, sometimes small, lying about in discrete irregular masses, and sometimes grouped into larger mulberry-like concretions, varying much in size.  These brain sand particles have become of practical importance in the detection of pineal disease because they, like all lime salts, will stop the X-rays, and so can be photographed.