RESPIRATION 277 



ject's mouth until the wash water gives no blue 

 color (iodide of starch) on the addition of potas- 

 sium iodide and concentrated nitric, acid (to set 

 free the iodine). Let the subject chew a small 

 piece of clean black rubber-tubing to increase 

 the secretion of saliva. At intervals of two 

 minutes, beginning with the swallowing of the 

 potassium iodide, empty the mouth into the cor- 

 responding test-tube, at once rinse the mouth 

 with water, and begin a fresh collection. 1 



Note the moment at which the drug appears 

 in the saliva. 



RESPIRATION 

 CHEMISTRY OF RESPIRATION 



Estimation of Oxygen, Carbon Dioxide, and 

 Water. 2 Weigh bottles 3, 4, and 5 (4 and 5 



1 If the saliva secreted during two minutes cannot be held 

 in the mouth with comfort and without loss by swallowing, the 

 mouth may be emptied into a freshly washed porcelain dish, 

 from which the saliva should be poured into the proper test- 

 tube at the end of each two-minute period. 



2 Apparatus. Two aspirator bottles, with box. A wooden 

 tray, containing a jar for the guinea-pig, and six bottles, viz. : 

 Nos. 1 and 4, filled with soda-lime, to absorb carbonic acid ; 

 Nos. 2, 3, and 5, filled with pumice stone soaked in sulphuric 

 acid, to absorb moisture ; No. 6, a Miiller valve, to prevent air 

 being forced back through the series of bottles by a wrong 

 coupling of the aspirator tubes. 



