382 THE CIRCULATION OF THE BLOOD. [CHAP. XXVIII. 



Hering was the first to experiment on this subject, his object 

 being to ascertain how soon a substance easily recognized (as ferro- 

 cyanide of potassium) , when introduced into one part of the circu- 

 lation, as the right jugular vein, could be detected in a distant part 

 of the circulation as the left jugular. Hering found that this sub- 

 stance would pass from the right to the left jugular veins in from 

 twenty to thirty seconds ; and from the jugular vein to the great 

 saphena in twenty seconds; from the jugular vein to the masseteric 

 artery in from fifteen to thirty seconds. Results quite confirmatory 

 have been obtained from like experiments by Poiseuille, and also 

 by Blake. The former found that ferrocyanide of potassium, 

 with acetate of ammonia, or nitrate of potash, passed from one 

 jugular vein to the other, in from eighteen to twenty- four seconds; 

 but that the addition of alcohol retarded the rate of transit to 

 from forty to forty-five seconds. Blake found that nitrate of 

 baryta passed from the jugular vein of a horse to the opposite 

 carotid artery in from fifteen to twenty seconds. He found also 

 that the poisonous influence of strychnia on the nervous system, 

 showed itself in twelve seconds after injection into the jugular 

 vein ; in a fowl, in six seconds and a half ; and in a rabbit in four 

 seconds and a half.* 



The results obtained from calculation as regards the rate of the 

 circulation, are less conclusive than those by experiments, for the 

 obvious reason that we have only the approximative value of the 

 two principal quantities which enter into the calculation, namely, 

 that of the mass of blood in the body, and that expelled at each 

 systole. But the results of the two modes of inquiry are suffi- 

 ciently near to each other, to denote that the round of the circula- 

 tion is completed by any given portion of blood in a marvellously 

 brief period, which, in man, probably, rather falls below than 

 exceeds a minute. We need not, therefore, have recourse to any 

 other hypothesis to explain the rapid effects of certain poisons, than 



weight of the body, and as from Volkmann's researches the quantity expelled 

 at each systole of the ventricle is 4 ^th of the weight of the body, calling this 



weight jo, then x = -p and y p, and t=;z P therefore t = SO z, whence 

 o 400 p 



it appears that the time of the circulation is directly as the duration of a 

 pulse, and inversely as its frequency. 



* Hering in Tiedemann and Treviranus Zeitschrift fiir Physiol. b. iii. Poi- 

 seuille's Ann. des Sc. Nat. 1843. Blake Edin. Med. and Surg. Journal, 1841. 

 See also on this subject Volkmann's ] Oth chapter. 



