WORK OF THE HEART. 185 



the potassium ferrocyanide is detected by adding ferric chloride to the 

 serum, which separates from the samples of blood after they have 

 stood for a time. The duration of the circulation is as follows : 



Horse, . . 31'5 seconds. 

 Dog, . . 167 

 Rabbit, . 7 '79 



Hedgehog, 7*61 seconds. 

 Cat, . . 6-69 

 Goose, . 10-86 



Duck, . .10-64 seconds. 

 Buzzard, . 6 '73 ,, 

 Fowl,. . 5-17 



Results. When these numbers are compared with the frequency of 

 the normal pulse-beat in the corresponding animals, the following 

 deductions are obtained : 



(1.) The mean time required for the circulation is accomplished 

 during 27 heart-beats i.e., for man = 23'2 seconds, supposing the 

 heart to beat 72 times per minute. 



(2.) Generally, the mean time for the circulation in two warm-blooded 

 animals is inversely as the frequency of the pulse-beats. 



Conditions Influencing the Time. The time is influenced by the 

 following factors : 



1. Long vascular channels (e.g., from the metatarsal vein of one foot to the 

 other foot) require a longer time than short channels (as between the jugulars). 

 The difference may be equal to 10 per cent, of the time required to complete the 

 entire circuit. 



2. In young animals (with shorter vascular channels and higher pulse-rate) the 

 time is shorter than in old animals. 



3. Rapid and energetic cardiac contractions (as during muscular exercise) diminish 

 the time. Hence rapid and at the same time less energetic contractions (as after 

 section of both vagi), and slow but vigorous systoles (e.g., after slight stimulation 

 of the vagus) have no effect. 



C. Vierordt estimated the quantity of blood in a man, in the following 

 manner. In all warm-blooded animals, 27 systoles correspond to the time for 

 completing the circulation. Hence, the total mass of the blood must be equal to 

 27 times the capacity of the ventricle, i.e., in man, 187*5 grams, x 27 = 5062-5 

 grams. This is equal to T V of the body-weight, in a person weighing 65 '8 kilos, 

 (compare 49). 



It is not to be forgotten that the salt used is to some extent poisonous (p. 108), 



93. Work of the Heart. 



Johann Alfons Bernoulli (1679) and Julius Eobert Mayer estimated 

 the work done by the heart. The work of a motor is expressed in 

 kilogramme-metres i.e. 9 the number of kilos, which the motor can 

 raise in the unit of time to the height of 1 metre. 



The left ventricle expels 0'188 kilo, of blood (Volkmann) with each 

 systole, and in doing so it overcomes the pressure in the aorta, which 

 is equal to a column of blood 3'21 metres in height (Donders). [The 

 amount of blood expelled from each ventricle during the systole is 

 about 180 grins. (6 ozs.) It is forced out against a pressure of 



