404 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1946 
ent through the use of electronic means. The complete lack of inertia 
in electronic equipment (at least so far as concerns the biological proc- 
ess to be measured), the ability to amplify, and the negligible amount 
of input power required to control electronic devices are, in part, 
reasons for the general anticipation of such a development. But bio- 
logical considerations also contribute good reasons for the adoption 
of electronic equipment. Of these reasons, one of the foremost is that 
minute voltages, called action potentials, are produced within the body 
as a result of biological activity of the heart, brain, or nerves, for ex- 
ample. The amplification, detection, and analysis of these action 
potentials has opened up new fields of diagnosis which have reached 
their most advanced developments in the fields of electrocardiography 
and electroencephalography. Moreover, it has been found that the 
electrical characteristics of the skin may be used for diagnostic pur- 
poses, and here again electronic equipment is called upon to play its 
important role. . 
In electrocardiography the action potentials generated in the body as 
the result of the beating of the heart are obtained from electrodes 
placed on the arms, legs, or chest of the patient. These minute volt- 
ages are then amplified and recorded. A deviation of the recorded 
curves from the normal pattern indicates a pathological alteration of 
the heart activity. Since the patterns for different diseases are known, 
a reliable differential diagnosis is usually possible. It has also been 
proposed to use these action potentials for therapeutic purposes, as, for 
example, resuscitation or the treatment of cardiovascular diseases. 
Pick-up electrodes, from which the action potentials are cbtained, are 
attached to the patient. After suitable amplification these potentials 
are reapplied to the patient by means of another pair of electrodes. By 
designing the amplifier for proper phase shift or delay of signals, it 
may be possible to stimulate the activity of the heart in its own rhythm. 
Tn this technique the heart is used as a self-excited oscillator. As yet, 
little is known about the results obtained with this method. 
The electrical activity of the brain is recorded by means of the 
electroencephalograph, which makes possible the diagnosis of certain 
mental disorders by means of electrical potential measurements on 
the scalp. The principle of the electroencephalograph is similar to 
that of the electrocardiograph. The interpretation of the curves, 
which are naturally much more complex than those of the electro- 
cardiograph, is, however, sometimes difficult. Considering the very 
complicated processes of the brain activity, we would expect this, but 
the difficulty is a particular challenge to obtain more and better infor- 
mation by the use of improved equipment. With this method it is 
now possible to determine the location of a brain tumor (sometimes 
very important in brain surgery), and it may become feasible to 
