142 FOURTH REPORT — 1834. 



the blood ; assisted also by pressure, Avhether atmospheric or 

 otherwise, on account of the disposition of the vah'es in the ar- 

 teries and in the veins ; that the vis a tergo is more effectual 

 during expiration ; and that the return of the blood to the heart 

 is facilitated by the emptj- state of the auricles and by inspira- 

 tion ; that the vital attraction and repulsion between the mole- 

 cules of the organs and of the arterial and venous blood is a con- 

 current cause. 



Hering has published some valuable experiments* made with 

 a view to determine the time in which the circulation is effected. 

 His method was to pour a solution of some harmless substance, 

 easy of detection by tests, as prussiate of potass, into a vein ; and 

 to determine, by observation of the blood taken from another 

 distant vessel at short intervals, how soon the presence of the 

 injected solution could be discovered in the latter. In Horses 

 it passed from one jvigular vein through the lungs and great cir- 

 culation, and Vv'as detected in the opposite jugular vein in a time 

 varying from 20 to 25 and from 25 to 30 seconds ; from the 

 jugular to the sapheena, in 20^; from the jugular to the external 

 maxillary artery, in from 10^ to 15% and in another instance 

 from 20^ to 25^; from the jugular to the metatarsal artery from 

 20' to 25% and from 25= to 30'; once it required 40'. 



From other experimentsf Hering has concluded that the ve- 

 locity of the blood is independent of the frequency of the heart's 

 action. The prussiate of potass was not detected more quickly 

 than usual when the heart's action had, in numerous instances, 

 been greatly quickened by infusion of tinct. of white hellebore, 

 camphorated spirit, &c. If, with Hales, we estimate the weight 

 of a horse at SOOlbs., and his blood at 40lbs., which is certainly 

 not too high an estimate, and allow ten ounces to be thrown 

 from the heart at each systole, (the greatest possible quantitj^,) 

 then 1"* 37^ will be the least time in which the whole mass of 

 the blood will go through the heart*. And though the circula- 

 tion consists not of one, but of many circles, the smallest being 

 that of which the course through the coronary vessels of the 

 heart forms part, and though each of these circles be performed 

 in a different time, yet it appears difficult to make any probable 

 supposition respecting the circuit taken by the substances in- 

 jected in the above instances which will satisfy the rapidity 

 with which they were detected. How then is their quick trans- 

 ference to be explained ? Probably, as is suggested by Miiller, 

 the foreign fluid diffuses itself through the mass of the blood 

 more rapidly than the latter circulates. 



* Zeitschrift fiir Physiologic, vol. iii. f Zeitschrift, vol. v. part 1. 



X Burdach. 



