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TEXT-BOOK OF PHYSIOLOGY. 



experiment the proximal bulb is filled with oil, the distal bulb with serum 

 or normal saline. On removing the clips on the artery the blood flows into 

 the proximal bulb and drives the oil into the distal bulb. As soon as the 

 former is filled with blood the bulbs are reversed and the same relative condi- 

 tions are attained. This is repeated a number of times. Knowing the 

 capacity of the bulbs, and the number of times they are filled in a given 

 period, the total quantity of blood discharged is obtained. This divided by 

 the sectional area of the artery gives the velocity. The following values 

 have thus been obtained: For the carotid of the dog, 205 to 357 mm. per 

 second; for the carotid of the horse, 306 mm.; for the metatarsal artery of the 

 horse, 56 mm. (Volkmann). For the carotid of rabbits, 94 to 226 mm.; for 

 the carotid of the dog, 349 to 733 mm. (Dogiel). 



The variations in the velocity of the blood in the arteries during the differ- 

 ent phases of the cardiac cycle have been determined by Chauveau and 



Lortet with the hematachometer 

 (Fig. 1 66). This consists of a me- 

 tallic tube carrying a graduated 

 disk. At one point the tube is 

 perforated but covered with a rub- 

 ber band through which passes an 

 index. When the tube is inserted 

 into the divided ends of an artery, 

 the current of blood strikes the 

 short arm of the index and gives to 

 the outer long arm a movement in 

 the opposite direction. The extent 

 of the excursion indicates the veloc- 

 ity. The apparatus is first grad- 

 uated with currents of water of 

 known velocity. With this instru- 

 ment Chauveau found that in the 

 horse the velocity during the systole 

 was 520 mm. per second, at the 



artery. C. Lateral tube connected with a manom- beginning of the diastole 22O mm. 



per second, and during the pause 

 150 mm. per second. 



The Velocity in the Capillaries. The rate of flow in the capillary 

 vessels cannot be experimentally determined. It has been estimated by 

 Vierordt at 0.5 mm.|per second in his own retinal capillaries; by Weber at 

 0.8 mm. In frogs the velocity can be fairly well determined by observing 

 the time required for a corpuscle to pass over one or more divisions of an 

 ocular micrometer. Weber calculated in this way that the velocity is 0.5 

 mm. per second. 



As the velocity varies inversely with the sectional area, it becomes possible 

 to approximately determine the relation of the sectional area of the capillary 

 system to that of the aorta from the above-mentioned velocities. If it be 

 assumed that the velocity in the aorta averages 300 mm. and in the capillaries 

 0.5 mm. per second, then the sectional area of the capillaries is to that of the 

 aorta as 600 to i. 



FIG. 1 66. THE HEMATACHOMETER OF CHAU- 

 VEAU AND LORTET. A, B. Tube inserted in 



eter. b. Index moving 

 brane, a. G. Handle. 



in a caoutchouc mem- 



