40 Gas Analysis. V 
rubber stopper until the point projects in the interior of the tube, 
and 0.25 cc. of the ferricyanide solution are injected. The 
needle is then carefully withdrawn. 
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Fic. 1. The blood gas diffusion tube. The plug of the stop-cock is 
bored only in a right angle, not in a T, so that only two of the openings 
are connected at once. The open end of the tube is graduated as shown. 
This end of the tube is closed with a rubber stopper cut to about a half 
or a third the usual length, so that the needle of a small all glass hypo- 
dermic syringe can be thrust through it. 
The tube is now placed for 5 minutes in a rotating apparatus 
(Fig. 2) consisting of a block of wood turning on an iron rod and 
belted to a slowly moving motor or shafting. There are a num- 
