PHYSIOLOGY OF TO-DAY
by E. KENNERLY JR MARSHALL.
PHYSIOLOGY, in brief, is the study of function as distinguished from structure. When the physiologist looks at a living organism, he asks, "What does it do and how does it do it? What are its various parts for and how do they perform their functions?" The knowledge which has accumulated in regard to function is of two kinds, descriptive and theoretical. The first consists in statements of facts, as, for example, that the heart beats, that stimulation of the vagus nerve causes a slowing of the heart beat, or that muscular exercise causes an increase in the breathing and heart rate. Such observations, if accurately made, are incontrovertible, as they are mere description. They may be simply qualitative or may attempt to describe the phenomena in quantitative terms. Much of the older physiology was necessarily of this type. But after a certain number of facts have been accumulated, it is essential for the progress of science that they be correlated and that explanations for the observed facts be sought. The more recent physiology has, in large part, been of this theoretical or explanatory nature.
There are, in general, two modes of approach in attempting to explain the function of any particular organ, to unravel the processes concerned in the functioning of that part. One of these involves studying its variations in function in the intact normal animal, while the other involves more or less interference with the normal animal by isolat-