CHAP. VI. DIGESTION. 115 



is insoluble in water, is supposed by many chemists to 

 differ from the casein of fresh rnilk. 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 

 clay 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-Seylei 

 and Lubavin* casein consists of an albuminous, with 



* Dr Lauder Brmtcn, ' Handbook for Phys. Lab p. 529 



