Cuap. VI. DIGESTION. 115 
is insoluble in water, is supposed by many chemists to 
differ from the casein of fresh milk. I procured some, 
consisting of hard globules, from Messrs. Hopkins and 
Williams, and tried many experiments with it. Small 
particles and the powder, both in a dry state and 
moistened with water, caused the leaves on which they 
were placed to be inflected very slowly, generally not 
until two days had elapsed. Other particles, wetted 
with weak hydrochloric acid (one part to 437 of 
water) acted in a single day, as did some casein 
freshly prepared for me by Dr. Moore. The ten- 
tacles commonly remained inflected for from seven 
to nine days; and during the whole of this time the 
secretion was strongly acid. Even on the eleventh 
day some secretion left on the disc of a fully re- 
expanded leaf was strongly acid. The acid seems 
to be secreted quickly, for in one case the secre- 
tion from the discal glands, on which a little 
powdered casein had been strewed, coloured litmus 
paper, before any of the exterior tentacles were 
inflected. 
Small cubes of hard casein, moistened with water, 
were placed on two leaves; after three days one cube 
had its angles a little rounded, and after seven days 
both consisted of rounded softened masses, in the 
midst of much viscid and acid secretion ; but it must 
not be inferred from this fact that the angles were 
dissolved, for cubes immersed in water were similarly 
acted on.~ After nine days these leaves began to re- 
expand, but in this and other cases the casein did not 
appear, as far as could be judged by the eye, much, if 
at all, reduced in bulk. According to Hoppe-Seyler 
and Lubavin* casein consists of an albuminous, with 
* Dr. Lauder Bruntcn, ‘ Handbook for Phys. Lab.’ p. 529 
