67 



around the spot, but the circulation in the rest of the web is 

 normal. If the injury has not been too severe, the circula- 

 tion may become re-established in the stagnated spots, and 

 the inflammatory appearances disappear. 



309. Pin out the two horns of the tongue and observe 

 that under the microscope. The tongue is at first pale but 

 soon becomes reddened as the vessels become filled with 

 blood. With a low power the peripheral zone in the arteries 

 and veins may probably be seen better here than in the web. 



310. Place the frog on its back, cut through the skin and 

 muscles on one side and draw out the mesentery and pin 

 out a loop of it under the field of the objective and observe 

 the circulation. The inflammatory phenomena can be well 

 seen in this preparation or that of the tongue. (309). 



XXIV. 



311. Experiments in reflex action. Pith a frog and place 

 it on its belly. Note the position of its fore and hind 

 limbs. Note the position of the head as compared with 

 a normal frog. Are there any respiratory movements 

 at the nostrils or throat ? 



312. Pull, very gently, one of the hind-limbs into an ex- 

 tended position and then let go. Does it return to its former 

 location ? 



313. Gently tickle one flank with a feather or blunt 

 needle. Is there any contraction of the muscles ? 



314. Pinch the same spot sharply with a pair of forceps. 

 Is there any movement of the leg of the same or opposite 

 side. 



315. Pinch the skin around the anus with a pair of for- 

 ceps. What is the effect upon the legs ? 



316. Place the frog on its back. Does it make an effort 

 to get into a natural position ? Does it show any sense of 

 equilibrium ? 



