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The preparation of a series of acyloxymethyl esters of D-a-ammobenzylpenicillin (ampicillin) is described. In vitro these esters are hydrolyzed to ampicillin by nonspecific esterases present in serum and various tissues from rat, dog, and man.Experiments performed with the hydrochloride of the pivaloyloxymethyl ester in laboratory animals and healthy volunteers show that this compound, after oral administration, is absorbed far more efficiently than ampicillin. After the absorption the compound is rapidly hydrolyzed to ampicillin with the result that high blood and tissue levels of the latter are attained.

Proficiency in a given performance is usually measured in terms of the speed and effectiveness with which the task is executed. The results of experiments on learning and practice would seem to indicate that such proficiency is influenced by four factors, each of which may vary independently: (i) the ease with which the individual motor adjustments are carried into effect, (2) the ease with which the elements calling for adjustment are discriminated, (3) the ease with which the recognized sensory elements lead over into appropriate reactions, that is, the facility of the associative and coordinating processes, and (4) the ease with which the shift between consecutive adjustments is made. In other words, the typical adjustmental situation calls for motor adjustment, sensory discrimination, association and shift.The factors mentioned pertain only to the perfection of necessary adjustments, while differences in proficiency have long been recognized to depend upon still another factor, the presence or absence of unnecessary reactions. In skilled performances there are always a certain number of 'random reactions' which tend to be eliminated with increased practise. This is true even in the simplest tasks where the reactions to be made are closely defined and well known to the subject. But while the importance of this factor is fairly obvious and has been duly recognized in practise and learning experiments, the same cannot be said of the other four factors, the significance of which is much more difficult to determine experimentally.

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