Cuar. VL] DIGESTION. 95 
Chemically Prepared Casein.—This substance, which is in- 
soluble 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 tentacles 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 discs of a fully re-expanded leaf was 
strongly acid. ‘The acid seems to be secreted quickly, for in 
one case the secretion from the discal glands, on which a 
little powdered casein had been strewed, coloured litmus 
paper, before any of the exterior tentacles were inflected. 
Some 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 beinferred 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 a non-albuminous, 
substance ; and the absorption of a very small quantity of the 
former would excite the leaves, and yet not decrease the 
casein to a perceptible degree. Schiff assertst—and this is 
an important fact for us—that “la caséine purifiée des 
chimistes est un corps presque complétement inattaquable 
par le suc gastrique.” Sothat here we have another point of 
accordance between the secretion of Drosera and gastric juice, 
as both act so differently on the fresh casein of milk, and on 
that prepared by chemists.t 
* Dr. Lauder Brunton, ‘Handbook that this difference is no doubt due 
for Phys. Lab.’ p. 529. to the action of the alcohol used 
+ ‘Leçons; &c. tom, ii. p. 153. in making ‘chemically prepared 
t [Professor Sanderson | tells me _ casein.’’—F. D. 
