ACTION OF GAITE'INE 243 



66). Place the frog in a battery jar and examine it from 

 minute to minute. Do you note any immediate symptoms? 

 Touch the muscles of the hind legs from time to time and 

 note any changes. Does the animal have convulsions? If 

 so, of what character are they? Keep the animal under 

 observation until it dies, watching the muscles carefully. 

 Do you observe any changes in these ? If so, what explana- 

 tion can you offer? 



EXPERIMENT XLIII. 

 Caffeine. (Frog: Muscle and Nerve.) 



1. Pith a frog and isolate both gastrocnemius muscles 

 and both sciatic nerves (attached to the muscles, i.e., nerve 

 muscle preparations). Determine the normal minimal 

 stimulation to cause contraction in nerve A and muscle B. 

 Pour a small amount of caffeine solution into each of 

 two watch glasses. Into watch glass A place the nerve 

 of one of the muscle nerve preparations and into watch 

 glass B place the muscle of the second preparation. 

 From moment to moment stimulate the nerve of prepara- 

 tion A and the muscle of preparation B with single shocks. 

 What action has caffeine on the vitality of nerve trunks 

 and of muscle? Which is affected first? Watcli the mus- 

 cle closely and note any gross changes in appearance, color, 

 length, solidity, etc. What do you observe? What ex- 

 planation can you offer? Tease out some small fibers from 

 muscle A and place them on a slide and examine with a 

 compound microscope. Can you see the cross striatlons 

 well? Cover the fibers with a cover glass and while watch- 

 ing the fibrils closely run a few drops of caffeine solution 

 under the edge of the cover glass in such a manner that 

 the solution reaches the fibrils you are watching. What 

 effect has this on the muscle fibers? How are the cross 

 and longitudinal markings affected? How do you ex- 

 plain this? 



