88 THE MECHANISM OF THE CIRCULATION. 



The primary elevation rapidly reaches its maximum, and is followed 



by a fall which is not found on the arterial tension curves. This 



fall closely resembles that on the velocity curves obtained with the 

 dromograph. 



THE CIRCULATION TIME. 



Ed. Hering injected a solution of potassium ferrocyanide into one 

 jugular vein of a horse, while from the opposite jugular vein he collected 

 samples of blood at intervals of five seconds. The samples thus obtained 

 were allowed to coagulate, and after expression of the serum the latter was 

 tested with ferric chloride. He found that in 20 to 30 seconds the salt is 

 received by the right heart, propelled through the lungs, received by 

 the left heart, and propelled through the carotid arteries and capillaries, 

 into the jugular vein. 1 So astounding a result was at first received with in- 

 credulity, but Bering's experiments were fully confirmed by Poiseuille 

 and Blake. 2 



After injection of barium nitrate into the jugular vein of a horse, 

 Blake obtained evidence of the presence of this salt in the carotid artery 

 on the opposite side in 15 seconds. Poiseuille 3 found that on employing 

 as an index weak solutions of ammonium acetate or potassium nitrate, 

 the circulation time was accelerated, while on the addition of alcohol 

 the period was lengthened. This agreed with results which Poiseuille 

 had obtained in investigations on the flow of water in capillary glass 

 tubes. By Vierordt 4 the experimental method was improved. He 

 affixed a number of small cups to a disc which was rotated at a 

 uniform and known rate. The blood, subsequently to the moment of 

 injection, was allowed to flow from the vein into these cups. Hermann 5 

 replaced the cups by a continuous sheet of filter-paper, which was 

 divided into sections corresponding to intervals of time. The venous 

 blood flowed in a continuous stream on to the filter-paper as the drum 

 rotated. At the end of the experiment the filter-paper was dried and 

 tested for the presence of the salt. The innocuous ferrocyanide of sodium 

 is more suitable than the potassium salt. Yierordt 6 determined the 

 circulation time in seconds in the following animals to be 



Squirrel . . . 4*39 Horse . . . 31 '5 



Cat . . . . 6-69 Cock . . . 5-17 



Hedgehog . . . 7'61 Duck . . . 10*64 



Rabbit . . . 7 '79 Goose . . . 10'86 



Dog .... 16-7 



The length of the circuit is found to make but little difference. This 

 is so because the time is chiefly spent in the passage of the blood, not 

 through the arteries and veins, but through the capillaries. Thus 

 Vierordt obtained the following mean results in four double determina- 

 tions : 



Jugular to jugular vein . . . dog 16*32 



Jugular to crural vein . . . . ,, 18*08 



Recently other ingenious methods of determining the circulation time 



1 Ztschr.f. PhysioL, 1829, Bd. iii. S. 85 ; 1833, Bd. v. S. 58. 



2 Win. Mcd. Journ., Oct. 1841, p. 104. 



' J Ann. d. sc. nat., Paris, Se"r. 2, ZooL, 1843, tome xix. p. 20. 



4 "Die Erschein. u. Gesetze d. Stromgeschwindigkeiten des Blutes ; " Frankfurt, 1858. 

 S. 56. 



5 Arch.f. d. ges. PhysioL, Bonn, 1884, Bd. xxxiii. S. 169. 



6 "Phys. d. Mensch.," 1861, S. 111. 



