Our plan was to illustrate the possibility of applying psychological experiments to the selection of fit applicants also in cases in which not one characteristic mental function stands out, but in which a large number of relatively independent mental activities are in play.  I choose as an illustration of such cases the work of the employees at the telephone switchboard.  A study of the psychological factors in this work is strongly suggested by the practical interests of the telephone companies, and may be looked on here exclusively from this point of view.  The user of the telephone is little inclined to consider how many actions have to be carried out in the central office before the connection is made and finally broken again.  From the moment when the speaker takes off the receiver to the cutting off of the connection, fourteen separate psychophysical processes are necessary in the typical case, and even then it is presupposed that the telephone girl understood the exchange and number correctly.  It is a common experience of the companies that these demands cannot be satisfactorily fulfilled when a telephone girl has to handle more than 225 calls in an hour.  The official statistics show that this figure is exceeded in not infrequent cases,[13] in extreme cases the number may even rise beyond 300.  Moreover, in short periods of reinforced demands it may happen that for a few minutes even the rapidity of 10 calls in a minute is reached.  Normally the burden is divided among the employees in such a way that about 150 calls fall to each one in an hour, and that this figure is passed considerably only in one morning and one evening hour.  A skillful distribution of pauses and ample arrangements for rest, usually together with very excellent hygienic conditions, make it possible for the fit persons to be able to carry on this work without over-fatigue from 8 to 9 hours a day.  On the other hand, it is only natural that such rapid and yet subtle activity under such high tension, where especially the quick localization of the correct hole is a difficult and yet indispensable part, can be carried out only by a relatively small number of human nervous systems.  The inability to keep attention at such a high point for a long while, or to perform such rapid movements, or to retain the numbers correctly, does not lead to fatal accidents like those in the case of the unfit motormen, but it does lead to fatigue and finally to a nervous breakdown of the employees and to confusion in the service.  The result is that the company is continually obliged to dismiss a considerable proportion of those who have entered the service and who have spent some months in going through the training school of the company.  As one single company, the Bell Telephone Company, employs 16,000 operators, the problem is an expansive one, and it has bearing on the health of the employees as well as on the patience of the subscribers.  But above all it refers to the economic interests of the company, inasmuch as every girl who