PERIODS OF PARTS OF THE CIRCULATION. 685 



injected into the right jugular vein of a horse, successive portions of 

 blood are drawn from the opposite jugular vein, and subsequently 

 tested; the presence of the salt has been detected in the portion of 

 blood so drawn, at the expiration of 30 or even of 20 seconds. (Hering.) 

 In such an experiment, the ferrocyanide of potassium could not have 

 passed through the tissues across the neck, from one vein to the other, 

 but must have proceeded with the blood along the right jugular vein, 

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

 to the left side of that organ, next through the aorta, carotid arteries, 

 and capillaries of the head and neck, and thence along the veins into 

 the left jugular; in other words, it must have performed, with the 

 blood, a complete circuit through the lesser circulation in the lungs, 

 and through that part of the greater circulation which belongs to the 

 head and neck. The passage of the ferrocyanide of potassium, from 

 the jugular vein, through the lungs, and thence, through the hinder 

 limbs of the horse, to the great saphenous vein of the thigh, takes 

 place in 20 seconds ; and, from the same vein, to various arteries of 

 the body, in still shorter times, viz., to one of the facial arteries in 

 10 seconds, but to more distant arteries, as e. </., to the metatarsal 

 in the hind limb, in from 20 to 40 seconds. (Hering.) 



Similar experiments have been made, but on an improved method, 

 by arranging a series of small cups on a rotating apparatus, so that 

 they can be quickly moved in succession, before an aperture in a vein ; 

 in this way, the blood is collected at very short and exact intervals. 

 The time occupied in a complete circulation of the blood, can thus be 

 determined even in small animals. In them, speaking generally, the 

 passage of poisonous substances injected into the veins, takes place 

 more quickly than in the horse. In the dog, the time is found to be 

 16.7 seconds ; in the rabbit, nearly 7.79 seconds ; in the cat, 6.69 

 seconds, and in the squirrel, 4.39 seconds; in the horse, it is 31.5 

 seconds. (Vierordt.) Allowing for the obvious effect of size, and con- 

 sequent length of the bloodvessels, it must be concluded that the blood 

 in the human body performs the complete round of the circulation, in 

 even less than half a minute. 



Yierordt has pointed out a remarkable relation between the frequency of the 

 pulse, that is, of the heart's beats, in different Mammalia and Birds, and the 

 ascertained average of the complete circulation in them. The frequency of 

 the pulse in these animals increases, generally, as their size diminishes, being, 

 for example, in the horse, dog, cat, rabbit, and squirrel, respectively, 55, 96, 

 240, 220, and 320 in the minute, or 60 seconds. But, as we have seen, the 

 times of a complete circulation in them are, 31.5, 16.7, 6.69, 7.79, und 4.39 

 seconds. From such data, it is shown, that a complete circulation, in these 

 several animals, is performed during the following numbers of heart's beats ; 

 viz., 28.8, 26.7, 26.8, 28.5, 23.7. Thus, in the horse, for example, as 60 sec. : 

 55 beats : : 31.5 sec. : 28.8 beats. In the larger Birds, nearly the same propor- 

 tion prevails ; and the mean relation is found to be about 27 heart's beats for 

 each complete circulation. 



In Man, Vierordt calculates that, with the pulse at 72 per minute, 

 the heart's beats are 27.7 for each complete circulation, which is 

 accordingly performed in 23.1 seconds, or less than half a minute. 

 Thus as 72 : 60 : : 27.7 : 23.1. 



