42 



EXPERIMENTAL PHARMACOLOGY 



tube to recorder 



oil enclosed 

 by membrane 



Fig. 17. Roy's kidney oncometer. 



Fig. 18. Arterial cannula. used also for injecting into veins. This is liy far the 

 best cannula for recording blood-pressure or injecting from a burette. Such cannulas 

 are made to order by glass-blowing firms (see page 515). The opening in the point 

 should be about 1/32, 3/64 or 1/16 inch in diameter for most purposes. The usual 

 difficulty is to get the smaller sizes. 



