215 
the pressure, nature, and area of the surfaces in contact. 
Hooks, in contact with one another, averaged after 3 weeks 138 “TE. Without eontact 190-145 
PP fF ioe " " n 5 ww 206.230. N y 146.1 
Removal of the epidermis from the concave surface acts as 
a weak stimulus. If a hook tendril, injured in this manner, is 
firmly attached to a fixed support, it coils, and increases in 
thickness much more than if without contact, but does not 
attain the same dimensions, that a normal hook in similar con- 
tact does. The antero-posterior diameter in such injured hooks 
is always slightly less than normal, in spite of the corky skin 
which may form over the injury, owing to the removal of the 
epidermis causing a partial drying and shrinkage of the cortical 
layer immediately beneath. 
Originally. Coils. 
Epidermis removed on concave surface. No contact. Averaged 
r 15 days 
150.169 [109.110] 1 
Epidermis removed on concave attached to fixed support. 
Averaged after 15 days 159. 185 ” 11/, 
Uninjured and without contact 118 . 140 ” Vy 
" attached to fixed support. After 5 weeks 420 . 405 " 2 
It is an interesting point to know, whether a strain, set 
up in a hook-tendril without any contact 
stimulus, in the strict sense of the term, 
being applied, will cause a thickening and 
curvature. This can be done by causing a 
hook, as in Fig. 3, to pull against a glass 
rod, covered with moist 10°/, gelatine, and 
fixed across an inverted shaded test tube, 
the mouth of which is closed by a moist 
plug of cotton wool. The difficulties are, 
that the pull on the rod can only be slight , 
whilst as the experiment must continue for 
at least 3 days, during this time the gelatine may dry up, or 
Fungi and Bacteria may develop in abundance, and cause me 
gelatine to melt. By changing the hook, however, every morning 
and evening with as little manipulation as possible, to a fresh 
gelatine covered rod, these latter dangers are avoided, and after 
