Suggestions have been offered in the preceding pages of concrete applications of endocrine knowledge to the understanding of behaviour, of the genius and commonplace, criminal and Puritan.  And in the chapter on historic personages, we tracked some of the story in detail.  This vein when explored will quarry untold riches.  It has been observed that financiers of mark, like great musicians, are special pituitary types.  Also that the financiers are voracious meat eaters and the musicians inordinately fond of sweets.  Differences in anterior and posterior predominances might account for this.  That we are playing here with no phantasy is proven by the fact that we can effect changes of tastes as well as of intellectual direction by appropriate feeding of various glandular extracts.  Just as much, indeed, as we can influence sex susceptibility, and the reaction to sex stimulation, by the artificial introduction from without of the proper hormones.

FATIGUE AND INDUSTRY

In industry, business and profession, the biologist will come more and more to be called as consultant.  Labor unions as well as the large employers of labor, and their employment managers have given much thought to the problem of fatigue.  Just what fatigue is, why different individuals tire at different rates, why some are constructed for monotonous routine while others must have constant variety and change, the relation to accidents and to quantity output, are a few of the major lines of inquiry upon which the endocrines obviously have a large bearing.  To the employment manager, labor turnover and the selection of personnel are adjacent fields of research.

Fatigue as an endocrine deficiency—­a depressed state of one or more of the glands of internal secretion, abolished when its normal functioning is restored—­is a general principle from which departures of exploration of sub-problems will proceed.  An endocrine organ will secrete at a certain rate.  When it is stimulated excessively, it will eject extra amounts of its secretion.  How long the period of excessive stimulation may last must depend upon the secretion potential or margin of reserve of the cells, varying from organ to organ, and from individual to individual.  After that, exhaustion and failure follows, with the onset of the symptoms of fatigue.

A pretty demonstration of this process has been worked out in the electrical stimulation of muscle.  If a muscle, say the biceps, is irritated by an electric current, it will contract.  As the strength of the current is increased, the degree of contraction becomes greater.  A sort of stepladder effect of increasing contractions may be thus obtained.  After a time, the electric shocks cannot cause a greater contraction, but only a lesser.  And if continued, the muscle will cease to function because of fatigue.  If now, when the muscle begins to lag in its response, and its contractions to decrease, one injects into