218 MANUAL OF PHYSIOLOGY. 



opacity depends on the fact that the blood, as will presently be 

 seen, is not a Ted fluid, but owes its color to the presence of solid 

 red particles or corpuscles which float in a clear, pale fluid. The 

 blood has a peculiar smell (halitus), distinct in different animals 

 and man, dependent on certain volatile fatty acids. Its specific 

 gravity varies from 1045 to 1075, the average being 1055. The 

 solid parts (corpuscles) are heavier (sp. gr. 1105) than the liquor 

 sanguinis (1027). 



When first shed the blood has a slippery feel, which it soon 

 loses, becoming sticky as it passes through the various stages of 

 the process of coagulation. 



AMOUNT OF BLOOD IN THE BODY. 



The total amount of blood has been estimated to be from y 1 ^ to 

 f-% of the body weight for an adult man, and somewhat less for a 

 new-born child. 



Much difficulty has been found in arriving at an accurate esti- 

 mation of the amount of blood in the body. In the first place, 

 all the blood cannot be made to flow out of the vessels of an ani- 

 mal when it is killed. Secondly, the quantity and quality of 

 blood are constantly varying with the capacity of the blood ves- 

 sels. Thirdly, when slowly withdrawn from the body during life 

 it is rapidly replaced by more fluid passing into the blood ves- 

 sels. This explains the enormous quantity of blood occasionally 

 reported to be shed in cases of bleeding to death. In these cases, 

 as quickly as the blood is lost, fluid is absorbed by the fine ves- 

 sels to replace it, so that if the bleeding be gradual the standard 

 quantity is still kept up in the vessels. Thus the very sudden 

 loss of a comparatively small quantity of blood may cause death, 

 whereas, if the bleeding go on sufficiently slowly and gradually, 

 as much, or even more, in quantity than normally exists in the 

 entire body may escape without fatal result, but of course much 

 of this is fluid which has recently entered the vessels to replace the 

 blood already lost. 



Weber's Method. The percentage of solid matters in the blood 

 is first carefully estimated. The absolute quantity of solids in 

 the drawn blood is then ascertained and added to the solids ob- 



