RETINAL CIRCULATION CHANGES 



171 



sels. Keep this observation carefully in mind for later 

 comparisons. 



Under the skin of the back inject with a hypodermic syr- 

 inge one cubic centimeter of four per cent chloral hydrate 

 solution. At intervals of five minutes or less again care- 

 fully observe the rate and appearance of the corpuscle flo\v 

 in the vessels previously examined. Does the frog become 

 deeply narcotized? How does chloral affect the heart! 



Fig. 164. Position and method used for observing the retinal circulation in a frog. 

 The ophthalmoscope shown in Fig. 163 is being used, but several other (cheaper) forms 

 of ophthalmoscopes are on the market and may be equally well employed. 



Are the muscular walls of the vessels- directly affected by 

 chloral hydrate? What conclusions can you draw from 

 this experiment? 



You may repeat this experiment using urethane or 

 paraldehyde or chloroform to anesthetize the frog if you 

 have time. Later in your course other drugs, such as nitro- 

 glycerine, amylnitrite, arecoline, atropine, etc., may also 

 be used in this experiment. 



