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The Relation of the Heart-Beat to Electrolytes and its 

 Bearing on Comparative Physiology. 



By 

 George Ralph Mines, * 



Fellow of Sidney Sussex College, Camhridge. 



An objection often raised to experiments on tissues treated with 

 artificial solutions and isolated from nervous control is that results 

 obtained under such highly abnormal conditions can be of no real 

 value. This criticism arises essentially from a misconception as to the 

 aim of the experiments in question, but it is encountered so frequently 

 that it may not be out of place to consider briefly why it is necessary 

 for the physiologist who would learn something of the more in- 

 timate mechanism of the cell to work with tissues under artificial 

 conditions. 



Let us suppose that the action of some chemical substance on the 

 heart-beat is the subject of investigation. It is found, we will suppose, 

 that on injecting a solution of the substance into the circulation of an 

 intact animal the beat of the heart is modified in some way — it may 

 be in frequency or force, or in the rhythmic sequence of its chambers. 

 If on repetition of this simple experiment, made on animals as far 

 as possible under normal conditions, the same result is consistently 

 obtained, the result may be of therapeutic interest. For its inter- 

 pretation in terms of what is already established about the mechanism 

 of the body, a searching physiological analysis is, however, required. 

 The effect on the heart may be direct or it may be due to one of a 

 variety of indirect actions of the substance. 



Thus, for instance, it may be due to an action of the substance — 



(1) on sensory nerve endings connected to the cardio-inhibitory 



or cardio-accelerator centres in the medulla ; 



(2) on the nerve cells in these centres ; 



(3) on cell stations in the course of the vagus or sympathetic 



nerves to the heart ; 



(4) on the respiratory movements, modification of which affects 



the condition of the blood in such a way as to influence the 

 heart, either directly or through action on tlie nerve centres 

 which can control it ; 



