rULMONAKY CAPILLARIES— SPHYGMOGHAPII. o21 



the vaso-motor centre and vessels, and begin artificial respira- 

 tion. We next note the blood-pressure, inject the poison, and 

 see what alterations it produces. Experiments may also be 

 made by irritating the vagus or ligaturing the aorta. 



Action of Siirroiindi7ig Paris. — It sometimes happens, as in 

 the case of physostigma, tliat the drug produces no contraction 

 in the vessels of the ear or mesentery when their nerves are cut 

 — a fact which shows that it acts on them through the vaso- 

 motor nerves, and not directly on their walls ; and nevertheless, 

 when injected into a vein after the cord has been cut, it may 

 cause the blood-pressure to rise very considerably. At first 

 sight, this would seem to indicate that the dru^? acted on the 

 walls of some vessels in the body, if not on those of the ear or 

 mesentery, directly, and not through their vaso-motor nerves. 

 On examination, however, it is found that the obstruction to 

 the flow of blood through the capillaries does not depend on 

 their contraction, but on the occlusion of a large number of 

 them in the intestine by spasmodic contraction of the intestinal 

 walls in which they are imbedded. 



Influence of the Pulmonary Capillaries. — It has lately been 

 pointed out by Holmes tliat when a drug such as ergot, 

 which acts on the walls of the vessels and causes them to con- 

 tract, is injected into the jugular vein, it has to pass through 

 the pulmonary capillaries before it reaches the systemic ones ; 

 and, by contracting them, it will lessen the amount of blood 

 sent into the aorta from the left ventricle, and will at first pro- 

 duce a fall in the arterial pressure, succeeded by a great rise 

 when time has elapsed for the drug to reach the systemic 

 capillaries and cause them likewise to contract. 



Use of the Sphygmograph. — For a description of the sphygmo- 

 graph and the mode of applying it, we must refer to the special 

 works on that subject, such as those of Marey and Sanderson. 

 The indications which it gives are the following : 1, The greater 

 or less pressure which is requisite to compress an artery and stop 

 its pulsations enables us to estimate approximately the amount 

 of pressure within it. 2. The amount of pressure and the 

 rapidity of the pulse help us to form conclusions regarding the 

 motor and inhibitory apparatus of the heart, in the same way as 



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