50 QUANTITY OF BLOOD. [BOOK I. 



The total quantity of blood present in an animal body is estimated 

 in the following way : As much blood as possible is allowed to escape 

 from the vessels ; this is measured directly. The vessels are then 

 washed out with water or normal saline solution, and the washings 

 carefully collected, mixed, and measured. A known quantity of blood 

 is diluted with water or normal saline solution until it possesses the 

 same tint as a measured specimen of the washings. This gives the 

 amount of blood (or rather of haemoglobin) in the measured specimen, 

 from which the total quantity in the whole washings is calculated. 

 Lastly, the whole body is carefully minced and washed free from blood. 

 The washings are collected and filtered, and the amount of blood in 

 them is estimated as before by comparison with a specimen of diluted 

 blood. The quantity of blood, as calculated from the two washings, 

 together with the escaped and directly measured blood, gives the total 

 quantity of blood in the body. 



The method is not free from objections, but other methods are open 

 to still graver objections. 



The blood is in round numbers distributed as follows : 

 About one-fourth in the heart, lungs, large arteries, and veins, 



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skeletal muscles, 



other organs. 



Since in the heart and great blood vessels the blood is simply 

 in transit, without undergoing any great changes (and in the 

 lungs, so far as we know, the changes are limited to respiratory 

 changes), it follows that the changes which take place in the blood 

 passing through the liver and skeletal muscles far exceed those 

 which take place in the rest of the body. 



