STUDIES IN THE PHYSIOLOGY OF BLOOD VESSELS IN MAN. APPARATUS AND METHODS. I. A SENSITIVE PLETHYS- MOSPHYGMOGRAPH FOR A PORTION OF THE FINGER1

The apparatus I wish to describe was designed the air space which comes in contact with the body for the study of volume changes due to varying part being observed; second, by change in shape degrees of fullness of the smaller blood vessels in and size of the fine recording capsule; third, by a portion of the human body, particularly for that lengthening or shortening the metal bellows in the portion of the finger distal to the major skin coarse recorder. Whenever the air space is en-creases at the terminal finger joint. croached upon by a slight swelling of the finger, The principal characteristics aimed at in devis- the recorder capsule bulges by an almost equal ing the apparatus and method were: 1. Accurate volume. The volume increase of the capsule is measurement should be possible for either quick slightly less than the volume increase of the finger volume changes due to the pulse when as small as due to the compression of the air in order to over-0.5 cu. mm. and of slower changes in volume of come the resistance of the capsule to distortion. relatively great magnitude, that is up to 800 cu. If the swelling of the body part is of great mag-mm. 2. Each type of measurement should be nitude, great distension of the capsule tends to oc-based on graphic records made simultaneously. 3. cur, but is prevented by the intervention of th