The application of a new biological heart-rate recorder to the study of the action on the frog heart of small doses of Crataegus, Digitalis, Strophanthus gratus and of trace doses of Strophanthus sarmentosus ^{[ * ]}

Summary

1. 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.

2. 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.

3. 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.

^* Read at a meeting of the Scottish Branch of the Faculty on December 17th, 1952.