VASCULAR SYSTEM 205 



end of the divided vagus is stimulated, the heart's action is 

 slowed down until the heart finally comes to a stop fully 

 dilated in diastole. From this one may conclude that nor- 

 mally the vagus transmits inhibitive stimuli which control the 

 heart, and that these, upon division of the vagus, no longer 

 prevent the heart from rapid beating. The division of one 

 vagus causes the blood pressure to fall, the division of both 

 causes a still further fall. 



The total volume of blood in man and various Vertebrates 

 bears the following proportion to the body-weight (Collin) : 



Adult man average one-thirteenth l 

 Horse one-eighteenth 

 Ox one-thirtieth j of the body- 

 Sheep, goat one-twenty-fifth ! weight, includ- 

 Pig one-twenty-eighth )- ing contents 

 Dog one-eighteenth ] of stomach 

 Cat one-twentieth j and intestine 

 Rabbit one-thirty-second 

 Birds one-twenty-ninth J 



The physical and chemical properties of the blood of man 

 and Vertebrates generally is fully described in the text-books 

 of physiology. 



The colour of the blood in all Vertebrates is red except in 

 the amphioxus. But apart from the difference in colour be- 

 tween arterial and venous blood many gradations in the 

 brightness of the arterial blood may be met with. Among 

 domestic animals it is brightest in the dog, darker in horses 

 and pigs, and darkest in oxen ; human arterial blood has its 

 own particular tint. 



There is something quite characteristic, although impossible 

 to describe, in the smell of the blood in different species of 

 animals ; the taste is saltish, the reaction alkaline. 



The specific gravity does not vary greatly : 



Man = 1055 



Horse, pig, dog 1060 



Goat = 1042 



Cat = 1054 



Rabbit = 1049 



