is spent in gathering evidence with the comparatively meager results that pass the tests. The burden added to the hospital laboratories by such work is very great, but the importance of the function cannot be overestimated, for it filters out what is useful and protects the profession from much that is worthless. The third category under which hospital laboratory work is carried on depends on the fact that every hospital is, or should be, an educational institution, and one of its primary duties is the instruction of all the members of the staff in the nature of disease. Many of the laboratory data, therefore, that fill the pages of carefully compiled hospital records do not have a direct diagnostic or therapeutic bearing on the individual case, but they contribute information which throws light on the pathological physiology and clarifies the disease process. In so far as the accumulation of such accessory laboratory observations is instructive to those who are studying the patients, the work is more than justified, but if, as sometimes happens, particularly with the younger members of the staff, it leads to the idea that all these observations are necessary for the proper diagnosis and treatment of any given case, the result may be most unfortunate. Properly used, such laboratory observations are enlightening and broadening; improperly used, they are blinding and narrowing. The real reason for taking an electrocardiogram on every patient with a cardiac arrhythmia is so that after one has studied the records of a large series of cases, he may understand the clinical manifestations of cardiac irregularities so well that he is able to recognize the type of arrhythmia without the electrocardiogram. His increased knowledge should, on the one hand, emancipate him from the need of the complicated apparatus in most cases, and, on the other hand, help him to appreciate the occasional case in which careful instrumental study is desirable. From this point of view, therefore, much hospital laboratory work may be regarded as of indirect significance for the individual patient, but aimed at the training of better clinicians. When, as sometimes happens, it results in the production of poor clinicians, unable to interpret disease except through the eyes of the laboratory, its purpose has failed, and failed seriously.