ACTION ON THE CAPILLARIES. 65 



amount of oscillation. In larger doses it almost invariably 

 increases the tension, sometimes very slightly, at other times 

 considerably ; and in one case of Mr. Blake's, Where he injected 

 it into the arteries, the rise was enormous, the maximum being 

 14 inches instead of 5. The tension attains its maximum in 

 three or four to nine or ten minutes, and then gradually dimi- 

 Fxishes. The oscillation is generally greater at first, and also 

 gradually diminishes. Sometimes there is a rise just before 

 death, and the tension diminishes very slowly after the heart has 

 ceased to beat. 



On the Capillaries. — In small doses, digitalis, while it slows 

 the heart's action, seems at the same time to contract the capil- 

 laries. If we look at the results of Exp. X, we see that, 

 although the cardiac pulsations were reduced from 140 to 78, 

 yet the mean tension remained the same. This can only be 

 explained by supposing that the capillaries are contracted, or 

 that the heart is sending in at each stroke nearly double the 

 amount it did before. This latter hypothesis seems extremely 

 improbable, for though the blood has longer time to collect in 

 the heart, yet we find when the same time is given by slowing 

 the cardiac pulsations directly, without any action on the 

 systemic capillaries, as we can easily do by galvanizing the 

 vagus, the arterial tension at once falls to a very considerable 

 extent. At other times we find that the tension not only does 

 not fall, but rises to a considerable extent, as in Exp. VI, where, at 

 3. 41' the number of pulsations was 85, and the mean tension 5"G5, 

 and at 4. 4' the pulse was 80, with a mean tension of 7 inches — 

 a fall of four beats, with a rise of nearly an inch and a half 

 Few observers, if any, have noted a higher rise of the arterial 

 pressure than Q^ inches, whicli was the maximum of oscillation 

 in this case, when they injected preparations of digitalis into the 

 veins, so that they passed through the heart first before getting 

 into the systemic circulation, but on one occasion in which 

 Mr. Blake injected infusion of digitalis into the carotid, pushing 

 it with some force, so that it entered into the systemic circula- 

 tion and had thus an opportunity of acting on the capillaries 

 before reaching the heart, the pressure rose to 12 or 14 inches. 

 From all these facts, I think we must conclude that it really 



