94 DROSERA ROTUNDIFOLIA. Cuap. VI 
leaf. These were examined after 21 hrs. 30 m., and all four 
were found rounded. After 46 hrs. the two cubes on the one 
leaf were completely liquefied, the fluid being perfectly trans- 
parent; on the other leaf some opaque white streaks could 
still be seen in the midst of the fluid. After 72 hrs. these 
streaks disappeared, but there was still a little viscid fluid 
left on the disc; whereas it was almost all absorbed on the 
first leaf. Both leaves were now beginning to re-expand. 
The best and almost sole test of the presence of 
some ferment analogous to pepsin in the secretion 
appeared to be to neutralise the acid of the secretion 
with an alkali, and to observe whether the process 
of digestion ceased; and then to add a little acid 
and observe whether the process recommenced. This 
was done, and, as we shall see, with success, but it 
was necessary first to try two control experiments ; 
namely, whether the addition of minute drops of 
water of the same size as those of the dissolved 
alkalies to be used would stop the process of diges- 
tion; and, secondly, whether minute drops of weak 
hydrochloric acid, of the some strength and size as 
those to be used, would injure the leaves. The 
two following experiments were therefore tried :— 
Experiment 6.—Small cubes of albumen were put on three 
leaves, and minute drops of distilled water on the head of a pin 
were added two or three times daily. These did not in the 
least delay the process; for, after 48 hrs., the cubes were com- 
pletely dissolved on all three leaves. On the third day the 
leaves began to re-expand, and on the fourth day all the fluid 
was absorbed. 
Experiment 7—Small cubes of albumen were put on two 
leaves, and minute drops of hydrochloric acid, of the strength of 
one part to 437 of water, were added two or three times. This 
did not in the least delay, but seemed rather to hasten, the 
process of digestion ; for every trace of the albumen disappeared 
in 24 hrs. 830 m. After three days the leaves partially re- 
expanded, and by this time almost all the viscid fluid on their 
discs was absorbed. It is almost superfluous to state that 
