76 



291. 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. 



292. 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. (291). 



XX 



293. 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? 



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

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

 location ? 



295. Gently tickle one flank with a feather or blunt 

 needle. Is there any contraction of the muscles ? 



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

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



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

 ceps. What is the effect upon the legs ? 



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

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

 equilibrium ? 



299. Pass a hook through its lower jaw and hang it to 

 the ring of a retort stand. How do the hind-limbs behave ? 



300. Pinch very gently the tip of one of the toes ; what 

 is the effect ? 



301. Fill two glasses, one with dilute sulphuric acid, the 

 other with water. Raise the glass containing the acid, until 

 the acid just touches the tip of the toes. Is the foot with- 

 drawn ? If so, raise the second glass and let the foot be 

 immersed in it, to wash off the acid. 



