CHEMICAL PROCESS OF RESPIRATION. 23 



LYMPH. 



Lymph or tissue juice resembles blood in being coagu- 

 lable and in containing colourless corpuscles. It differs 

 from it in being of lower specific gravity, in the tardiness 

 with which it coagulates, in the absence of blood-disks, and 

 consequently of haemoglobin, and in its containing rela- 

 tively to its weight less proteid, more urea and other 

 extractives, more sodic carbonates, and in yielding to the 

 mercurial vacuum more CO 2 . Its corpuscles are derived 

 partly from the tissues, but chiefly from the lymphatic 

 glands. 



Chyle differs from lymph chiefly in respect of the larger 

 proportion of fat (about I per cent.) which is present in it. 

 Each of the minute granules to which chyle owes its 

 opacity consists of a fat particle enclosed in an envelope 

 of proteid. 



CHEMICAL PROCESS OF RESPIRATION. 



In respiration each quantity of air respired undergoes 

 the following changes : Its oxygen is diminished by about 

 a quarter, viz., from 21 per cent, to 16 per cent. Its CO 2 

 is increased a hundred-fold, viz., from about 0^04 per cent. 

 to over 4 per cent. It becomes nearly saturated with 

 moisture. It acquires nearly the temperature of the body. 

 It becomes more or less charged with organic impurity, 

 acquiring thereby a peculiar smell. Its volume is dimin- 

 ished by -g-J-o or thereabouts. Its weight is increased in 

 proportion to the weight of CO 2 discharged. 



The percentage of CO 2 is dependent on the length of 

 time that the expired air has remained in the respiratory 

 cavity. (It can be increased by voluntary retention to 7*5 

 per cent.) Consequently, as the frequency of respiration 

 increases the percentage diminishes, though the total dis- 

 charge increases. 



