The past two and one-half decades have brought revolutionary changes in medicine. A number of us can remember clearly when a blood count was a highly scientific procedure and when the number of physical and chemical measurements designed to elucidate the manifestations of disease or even to be employed in research was limited, and viewed from the standpoint of the present-day superiority those methods were of questionable utility. So rapidly and yet so insidiously has the situation changed that it is difficult to trace even approximately the steps that have led up to the present position. One by one methods have been devised to supply data from physical and chemical analysis of body fluids and secretions or from biologic experiments; the application of these methods has served to produce an enormous literature the volume of which is ever increasing in almost geometric progression.
To attempt to analyze the factors responsible