Chap. VI.] DIGESTION. 95 



globules, more or less aggregated together, with no trace of 

 casein. As I was not familiar with the microscopical ap- 

 pearance of milk, I asked Dr. Lauder Brunton to examine 

 the slides, and he tested the globules with ether, and found 

 that they were dissolved. We may therefore conclude that 

 the secretion quickly dissolves casein, in the state in which 

 it exists in milk." 



Chemically Prepared Casein. This substance, which 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 

 pjowder, both in a dry state and moistened with water, caused 

 the leaves on which they were placed to be inflected very slow- 

 ly, generally not until two days had elapsed. Other parti- 

 cles, 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 re- 

 mained 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 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 a non-albuminous, 

 substance; and the absorption of a very small quantity of 



'* [Professor Sanderson has nncleln. which Is entirely ln<'l- 

 Cftlled my attention to the fact gentlMe by frastric Juice. F. I>.1 

 that the casein of cow's milk ' Dr. I-nnder Prnnton. ' Hand- 

 contains h sniull pruporllou of book for I'hys. Lab.,' p. 520. 



