BY DR. MICHAEL FOSTER. 409 



Repeat the observation on the other leg. Only that leg, the 

 toes of which are pinched, is drawn up: and if the toes be not 

 too roughly treated, no other movement than the drawing up 

 of the leg is witnessed. 



Obs. IV. With more force pinch the folds of the skin around 

 the anus. Both legs will be suddenly completel}' drawn up, 

 so that the toes of both feet are brought above the forceps, and 

 are then as suddenly and completely extended again. This 

 movement of sudden flexion and extension, that is of kicking, 

 may be repeated rapidly several times as the result of one for- 

 cible pinching of the region in question. 



06. V. Pinch with some force the skin at a point on one 

 side of the loins. The leg of the same side will be suddenly 

 flexed over the back, and brought round back again with a 

 sweeping movement. 



06. VI. The hind limbs hanging down as before, place a 

 watch or other small glass containing very dilute sulphuric 

 acid (one drop to 20, 30, or 50 CC m , strong enough to give an 

 acid. taste) underneath the frog, and bring it close up to one 

 of the feet, so that the extreme tip of the longest toe just dips 

 into the acid. Within a short time, the exact length of time 

 being determined by the strength of the acid and the condition 

 of the frog, the leg will be flexed, and the foot withdrawn. 

 Very frequently the movement, even after the fluid has been 

 taken quite out of the wa} r , is not confined to a single flexion 

 followed by a relaxation, but consists of a series of flexions 

 and relaxations, each succeeding flexion being less marked than 

 its predecessor. 



Repeat the observation with varying degrees of acidity, 

 beginning with simple distilled water, and gradually adding 

 acid. Be careful to wash the foot carefully with water after 

 each observation, to wait some minutes between each applica- 

 tion, and to dip only the tip of the toe, and that to the same 

 extent in each case. 



Measure by means of a metronome, beating very rapidly, the 

 exact time intervening between the actual entrance of the toe 

 into the fluid, and its withdrawal. 



With an acid of a gU-en strength, applied to the same frog 

 under varying circumstances, the duration of this interval may 

 be taken as a measure of the power of reflex action. The shorter 

 the interval, the more prone is the cord to reflex actions. In 

 making observations on the length of this interval, it is as well 

 to use very dilute acid, such as will only just give a sensation 

 of acidity when applied to the tongue. 



Obs. VII. Simple water of a sufficiently high temperature 

 (25-35C.) may be used instead of the acid. It has the ad- 

 vantage of being less likely than the acid to produce a perma- 

 nent action on the skin. The difficulty, however, of keeping 



