Summary
A recently developed electronic integrating heart-rate recorder for the exposed frog
heart is described and its use illustrated. This recorder has the advantages that
it is capable of dealing with low heart rates and of giving fine line recording instead
of the usual broad line due to wide pointer swing at each beat. It has a wide scale
and linear calibration allowing direct visual reading of very small rate variations.
It is constant in action and can run continuously for several days. By using frequency
selection of the e.c.g. harmonics A.C. interference is greatly reduced. Combined with
this is apparatus for the simultaneous registration of the electrocardiogram and of
the mechanical recording of the heart contraction in such a way as to avoid distortion
of the e.c.g. by continued monophasic injury currents. The accuracy of the rate recorder
and the registration of the e.c.g. with minimal distortion enables very small changes
to be demonstrated.
The application of these electronic methods to a study of controls and of drug applications
is discussed and illustrated. Criteria for assessing evidence of drug effects are
arrived at by using varying doses of macerations of Digitalis folium, Crataegus berries and Strophanthus gratus seeds.
The use of the criteria in estimating the results of drug and control applications
is also illustrated from records of the action of doses of water soluble extractive
of Strophanthus sarmentosus seeds representing from 6 mgm. to 0·15 mgm. of the seeds in Ringer solution, and
from “trace doses” in dilutions of the primary solutions of an order ranging from
10−6 to 10−11 prepared in distilled water.
Experiments were carried out on 367 frogs.
