314 PHYSIOLOGY. 



stromuhr, or rheometer. This instrument consists of two glass 

 bulbs, 1 and 2, of the same capacity. The ends of these glass bulbs 

 have a common opening above; below they are fixed, at 5-5', into 

 a metal disc. This disc rotates around the disc, 6-6" , so that after 

 a complete revolution a bulb, 1, communicates with a cannula, 9, and 

 another bulb, 2, communicates with another cannula, 8. This can- 

 nula, S, is fixed in the central end and the other cannula, 9, in the 

 peripheral end of the artery (carotid) ; the bulb, 1, is filled with oil; 

 the bulb, 2, with defibrinated blood. At a certain time the com- 

 munication through 8 is opened, the blood flows in, pushing the oil 

 before it and passes into 2, while the blood passes through 9 into the 

 peripheral part of the arten^. As soon as the oil reaches 4., the time 

 is noted, and bulbs 1 and 2 are rotated so that 2 takes the place of 

 1, and the oil is pushed back into 1 again. The quantit}^ of the 

 blood which passes in a given time is calculated from the time neces- 

 sary to fill the bulb. 



Hiirthle has invented a recording rheometer which indicates the 

 quantity of blood that enters and leaves the rheometer. Other instru- 

 ments have received the names Jicematachometer, hcemadromometer, 

 dromograpli, etc. 



Rate in the Veins. Whenever the total area of cross section of 

 the vascular tree increases, the velocity of its contained blood-cur- 

 rent diminishes; conversely, as the cross section diminishes the flow, 

 becomes proportionately more rapid. The total section of the sys- 

 temic arterial tree reaches its maximum extent in the arterioles and 

 capillaries. Along the venous tree the cross section diminishes as 

 the heart is neared, but never becomes as small as that of the 

 arteries. Therefore, the greatest velocity must exist in the arteries, 

 the least within the capillaries, while the mean between the two 

 extremes is that within the veins. 



Since the venous cross section diminishes as the heart is neared, 

 the velocity of its blood-current becomes heightened accordingly. 

 However, the average rate of venous blood-flow has been estimated 

 to be about 9 inches per second. 



Burton-Opitz with Hiirthle's instrument found the average rate 

 of flow in the femoral vein of dogs to be 61.G millimeters per second, 

 whilst in the external jugular he found it to be 147 millimeters per 

 second. Stimulating the vagus arrested the flow in the jugular. The 

 flow of blood in the external jugular was intermittent, due to two 

 types of variation, those caused by respiratory movements and those 

 produced by changes in pressure during each auricular cycle. Inspira- 



