5G ON DIGITALIS, WITH SOME OBSERVATIONS ON THE URINE. 



possesses the power of contracting the capillaries which Mr, 

 Blake assigned to it. 



As the poisonous action of digitalis becomes more fully de- 

 veloped, the capillaries become dilated (and probably paralysed), 

 the arterial tension falls, and, there being less resistance, the 

 heart's action becomes pari passu (Bouley and Eeynal) more 

 violent, while the arterial pulse becomes more weak and small, 

 and often seems rather a kind of indistinct wavering than 

 decided strokes. The objection may be raised that this is due 

 to the rapidity of the pulse, and the small size of the waves of 

 blood ; but we find that the heart is acting powerfully, and if 

 the capillaries were either of the same size or contracted, the 

 impulse being brisk, the waves of blood, however small, would 

 each give a distinct stroke to the finger, as is shown by Marey.* 

 Owing to this dilatation of the capillaries, and the easy transit 

 of blood through them, we find that almost immediately after 

 death the arterial system is empty, and the venous full and 

 turgid. From the patency of the capillaries less of the force 

 of the heart will be expended in forcing the blood through them, 

 and we would expect to find a higher pressure in the veins, at 

 least if the heart be not much weakened. This 1 have not yet 

 been able to determine. It would be well also to see, in the 

 web of a frog's foot, the changes caused by digitalis when 

 applied locally or generally. 



Occasionally, however, at or immediately before death, this 

 relaxed state of the capillaries seems to give place to one of 

 spasm, so that the arterial tension rises and cuntinnes at the 

 same height for a considerable time after the heart has ceased 

 to beat, diminishing very slowly as in Exps. IV and VI. This 

 could not possibly be owing to clots forming in the apparatus^ 

 at any rate in VI ; for if the tube had been stopped by one, the 

 two columns of mercury would have found their level by the 

 higher column decreasing, while the lower rose, and not by the 

 upper one remaining stationary, while the lower one rose up to 

 its own level. 



Of the changes in the cranial circulation, caused by digitalis 

 I can say nothing, several trials which I made on animals to 

 trephine and lute in a glass plate having proved total failures. 



"* Marey, op c!t., p. 243. 



