94 DROSERA ROTUNDIFOLIA. [Cuar. VI. 
getically than pure gelatine or isinglass; but I am assured 
by good authorities that it is most difficult;-or impossible, to 
know whether chondrin is pure, and if it contained any albu- 
minous compound, this would have produced the above effects. 
Nevertheless, I have thought these facts worth giving, as there 
is so much doubt on the nutritious value of gelatine; and Dr. 
Lauder Brunton does not know of any experiments with re- 
spect to animals on the relative value of gelatine and chrondrin. 
‘ Milk.—We have seen in the last chapter that milk acts 
most powerfully on the leaves; but whether this is due to 
the contained casein or albumen, I know not. Rather large 
drops of milk excite so much secretion (which is very acid) 
that it sometimes trickles down from the leaves, and this is 
likewise characteristic of chemically prepared casein. Minute 
drops of milk, placed on Jeaves, were coagulated in about ten 
minutes. Schiff denies* that the coagulation of milk by 
gastric juice is exclusively due to the acid which is present, 
but attributes it in part to the pepsin; and it seems doubtful 
whether with Drosera the coagulation can be wholly due to 
the acid, as the secretion does not commonly colour litmus 
paper until the tentacles have become well inflected ; whereas 
the coagulation commences, as we have seen, in about ten 
minutes. Minute drops of skimmed milk were placed on the 
discs of five leaves; and a large proportion of the coagulated 
matter or curd was dissolved in 6 hrs. and still more com- 
pletely in 8 hrs. These leaves re-expanded after two days, 
and the viscid fluid left on their discs was then carefully 
scraped off and examined. It seemed at first sight as if all 
the casein had not been dissolved, for a little matter was left 
which appeared of a whitish colour by reflected light. But 
this matter, when examined under a high power, and when 
compared with a minute drop of skimmed milk coagulated 
by acetic acid, was seen to consist exclusively of oil-globules, 
more or less aggregated together, with no trace of casein. 
As I was not familiar with the microscopical appearance 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.t 
* ¢Lecons,’ &c. tom. ii. p. 151. ‘of cow’s milk contains a small pro- 
+ [Professor Sanderson has called ~ portion of nuclein, which is entirely 
my attention to the factthat the casein ~ indigestible by gastric juice—¥. D.], 
