October 11, 1901.] 



SCIENCE. 



569 



ries ; those on the distal side of the resist- 

 ance are the veins. The side branch sub- 

 stitutes a wide channel for the narrow ones 

 and thus is equivalent to a dilatation of 

 the vessels. Between the pump and the 

 outlet valve is a side tube leading to a 

 membrane manometer which records the 

 changes in the pressure within the pump 

 (the loss in conveying the pressure through 

 the short wide connecting tubes may be neg- 

 lected). A mercury manometer is placed 

 between the pump and the capillary resist- 

 ance, to measure the arterial pressure, and 

 a second mercury manometer on the distal 

 side of the capillary resistance to measure 

 the venous pressure. 



The device used for the aortic valve is 

 shown in Fig. 3. A small glass tube is 

 fastened in a larger glass tube by a collar 

 of rubber tubing. The small glass tube is 

 closed at one end. One side is pierced 

 with a valve hole. The valve hole is closed 

 by a piece of rubber tubing which is drawn 

 over the small glass tube, and the middle 

 portion of the rubber tubing is cut away 



Fig. 3. The modified Williams' valve of the cir- 

 culating scheme. 



except over the hole. During the stroke 

 of the pump the water enters the small 

 glass tube under pressure, lifts the rubber, 

 escapes through the valve hole, and is car- 

 ried off by the large glass tube. "When the 

 pressure in the small glass tube is no longer 

 as great as that in the surrounding large 

 glass tube the rubber shuts the valve-hole. 

 Backflow is thus prevented. The mitral 

 valve is similar to the aortic, but the posi- 

 tion of the small glass tube is reversed. 



With this apparatus the physical phe- 

 nomena of the circulation may be learned 

 thoroughly. The conversion of the inter- 

 mittent into a continuous flow, the relation 



between rate of flow and width of bed, the 

 relation of peripheral resistance to blood- 

 pressure, the inhibition of the ventricle, the 

 opeoing and closing of the aortic valve, the 

 period of outflow from the ventricle, the 

 pulse wave, the physical phenomena of the 

 circulation in fevers and in aortic and mitral 

 regurgitation and stenosis, may all be 

 studied by the graphic method. Excellent 

 pulse curves may be obtained by placing a 

 sphygmograph upon the aortic tube. 



I first described the circulation scheme in 

 ' The Introduction to Physiology,' January, 

 1900. Its use during two j^ears by large 

 numbers of students in the Harvard Medical 

 School has suggested certain changes which 

 enable the apparatus to be more quickly put 

 together. In making these changes I have 

 been much helped by the criticism of Mr. 

 F. H. Pratt, Dr. W. B. Cannon and others 

 of my associates.* The accompanying fig- 

 ures show the most recent form of the ap- 

 paratus. 



III. THE MOIST CHAMBER. 



The moist chamber, shown in Fig, 4, pro- 

 vides for the study of the electrical proper- 

 ties of nerve and muscle under conditions 

 that prevent the stimulation caused by dry- 

 ing. It consists of a porcelain plate which 

 bears near the margin a shallow groove. In 

 this groove rests a glass shade which for the 

 sake of clearness has been omitted from 

 Fig. 4. To the porcelain plate is screwed 

 a rod, by which the plate may be supported 

 on a stand. Within the glass shade a right- 

 angled rod carries a small clamp, composed 

 of a split screw on which moves a nut, by 

 means of which the femur of a nerve muscle 

 preparation may be firmly grasped. The 

 holder for the split screw is arranged to 

 permit of motion in all directions. The 

 right-angled rod also carries two or more 

 unpolarizable electrodes. Each of these is 



* To Mr. Pratt's skilful hand I am indebted for the 

 drawings from which Fig. 2 and Fig. 3 were made. 



