204 THE HUMAN SPECIES 



in ruminants it is hardly visible on account of the thick layer 

 of thoracic muscles. The frequency or rate of the heart-beat 

 varies with the size of the animal ; the following figures are 

 those of Sussdorf : l 



Elephant .... 25-28 per minute 



Horse ..... 26-40 ,, ,, 



Ass . ... 46-50 



Ox . 40-50 

 Sheep "j 



Goat } 70-80 



Pig J 



Dog . 90-100 



Cat 120-140 



Rabbit 120-150 



Birds 120-180 



In man the rate varies, according to size and weight, from 

 seventy to seventy-five. 



The time occupied in complete circulation of the blood is, 

 according to Vierordt : 



Dog ..... 15-17 seconds 

 Goat . . . . 14 



Rabbit . 8 



Squirrel . . . 4? , 



Man 23 



The average blood pressure is as follows : 

 In the human aorta . . . about 180 mm. Hg. 

 carotid of horses . . . 150-190 

 dog . 120-170 



sheep . 170 



cat 150 



,, rabbit . . . 90-110 



The radial pulse of an adult man averages seventy-two 

 beats per minute, and of a woman a beat or two more. 



The nerve-supply of the heart is derived from the vagus, or 

 tenth cranial nerve, together with fibres from the sympathetic. 

 Division of the vagus in man, dogs and cats causes an extra- 

 ordinary increase in the heart's frequency, but if the peripheral 



1 Sussdorf in Ellenberger's Physiologic, ii., p. 239. 



