ACTION OF CHLORAL HYDRATE 169 



Save all the frogs until next day and note all later symp- 

 toms. How does the length of duration of the anesthesia 

 compare with that produced by ether or chloroform? Do 

 any of the frogs recover? If not, smaller doses may be 

 tried again. 



EXPERIMENT XVIII. 

 Chloral Hydrate. (Action on the Frog's Heart.) 



1. Pith a frog and arrange for recording heart tracings 

 (see Fig. 63). Obtain one or two normal tracings (show- 

 ing the effect of vagus stimulation). Start a new round on 

 the drum and apply four per cent chloral hydrate solu- 

 tion to the heart with a medicine dropper. Stimulate the 

 vagus nerve from time to time and note any changes. Con- 

 tinue the application of the drug until the heart stops. 

 Time the record and draw three or four horizontal com- 

 parison lines around the drum between the records. These 

 lines are made by rotating the drum by hand while a sta- 

 tionary tambour pointer or signal magnet pointer marks 

 on the drum. How did the drug affect the tonus of the 

 heart muscle? Was the inhibitory apparatus affected? 

 Examine the condition of the auricles and ventricle. 



EXPERIMENT XIX. 



Chloral Hydrate. (Frog: Retinal Circulation With the 



Ophthalmoscope. ) 



1. Examine carefully an ophthalmoscope (Fig. 163). 

 Fasten a frog to a board as shown in Fig. 164. Then with 

 the ophthalmoscope look into the frog's eye from a posi- 

 tion in front of the animal, but slightly from above and 

 from the side. Turn the lenses in the instrument until you 

 find one that permits you to see the red blood vessels in 

 the fundus of the eye. Examine these carefully. Can you 



