193 
depends to a certain extent upon the nature of the body in 
contact, and also upon the part of the hook which is stimulated , 
as well as upon the pressure, and the amount of surface irritated. 
Uncaria sclerophylla. The numbers in brackets give the aver- 
ages for the opposite untouched hooks. 
Wire bound round hook 
exerting moderate pressure 
Loose loop of twine. 
Weight 0 
on back only. 6 weeks, 
.2 grm. 
Loose loop of Cu wire. 
After 3 weeks. - 
ter 3 weeks. 
8—S A—P 8—S A—P S—S A-—P 8-8 A-—P 
215 . 475 [185 . 445] 0.5 grm. in 2 loops. 300 . 550 [175 . 485] 
P Bee A 
S—S A—P s— 
195 . 420 [150 . 380] 175 . 360 [150 . 350] 275 . 500 [240 . 465] 
After 5 weeks. 0.25 grm. 1 grm. in 6 loops. 150 . 335 [140 . 315] 
930. 480 [145 . 415] | 200.510 [180.460] | 150. 415 [130 . 370} 
After 5 weeks. 0.1 grm.* | 5 weeks. 1 loop. 0.3 grm. | 145 . 340 [115 . 290] 
160 . 355 [120 . 305] 160 . 350 [135 . 295 215 . 460 [195 . 430] 
5 weeks at extreme tip. 0.1-grm. in 1 loop. 
0.2 grm. fF 
130 . 305 [135 . 310] 120 . 350 [125 . 340] 
At * the stimulus is evidently very nearly a minimal one, 
and since a weight of 0.1 grm. can hardly set up any appreci- 
able strain in so thick and stout an organ as the hook of Uncaria, 
the slightly increased growth is probably due to the stimulus 
of contact alone. Also + shews that the extreme tip of the hook 
is not perceptibly sensitive to direct contact. Other things being 
equal a rough surface exerts a more powerful stimulating action , 
than a smooth one. Thus a single loop of Cu wire weighing 
0.1 grm. is a subminimal stimulus. 
To contact alone, the concave surface of the hook is the most 
irritable, the sides being also somewhat irritable, but the back 
hardly at all. If, however, the pressure applied be strong enough 
to set up a distinct strain in the hook, a marked and general 
response is obtained, no matter to what part of the hook the 
contact is applied In such cases, the most marked growth takes 
