THE CIRCULATION. 



physiological reactions to take place with rapidity and 



though the movement of the blood in these vessels, 



slow, yet as the distance between the arteries and the veins is very 



small, it requires but a short time for the blood to traverse the capillary 



system, and commence its returning passage by the veins. 



General Rapidity of the Circulation. 



The rapidity with which the blood passes through the entire round 

 of the circulation has been demonstrated by Hering, Poisseuille, 

 Matteucci, and Yierordt in the following manner : A solution of potas- 

 sium ferrocyanide was injected into the right jugular vein of the horse, 

 at the same time that a ligature was placed on the corresponding vein 

 of the opposite side, and an opening made in it above the ligature. The 

 blood flowing from this opening was received in separate vessels, at 

 intervals of five seconds, and afterward examined. The blood drawn 

 from the first to the twentieth second contained no trace of the ferro- 

 cyanide ; but that which escaped from the twentieth to the twenty-fifth 

 second showed unmistakable evidence of its presence. During this 

 time therefore the foreign salt must have passed from the point of in- 

 jection to the right side of the heart, thence through the pulmonary 

 circulation to the left side of the heart, outward by the arteries to 

 the capillaries of the head and neck, and thence down toward the heart 

 by the opposite jugular vein. 



Further observations have shown that the duration of the circulatory 

 movement varies somewhat in different animals ; being, as a general 

 rule, longer in those of larger size. Their main result, as given by 

 Milne Edwards,* is as follows : 



DURATION OF THE CIRCULATORY MOVEMENT. 



In the Horse 28 seconds. 



" Dog . . . . 15 " 



" Goat 13 " 



" Rabbit ........ 7 " 



In experimenting on the dog, by injecting a solution of potassium 

 ferrocyanide into the jugular vein, and immediately drawing blood 

 from the corresponding vein on the opposite side, we have found that 

 the short time required for closing the first vein by ligature after mak- 

 ing the injection, and opening the second to obtain a specimen of blood, 

 is sufficient for the passage of the ferrocyanide. If we regard the 

 duration of this movement in man as intermediate between that in the 

 dog and the horse, according to the difference in size, this would give 

 the time required by the blood to make the complete circuit of the 

 vascular system as not far from 20 seconds. 



. . 



* Lemons sur la Physiologic. Paris, 1859, tome iv., p. 364. 



