116 



EXPERIMENTAL PHARMACOLOGY 



Keep a record of these periods of time. Does the frog 

 again become completely normal? 



3. Place another frog in the milk bottle. Xow inject C0 2 



Oxygen 



-Leather washer- 



Nitrous 



oxid 



^ 



Fig. 112. A double yoke for holding gas tanks. Made by bolting together two bars 



of iron. 



Fig. 113. Yoke for holding gas tanks. Made of gas piping and fittings (see chapter 



on shop work). 



into the bottle. This may be done from a tank or from a 

 Guthrie generator (Fig. 11-1). Observe the effect on the 



