82 Brown. — On the Existence of a Semi-permeable Membrane 
were cut, however, a difference was observed in the conditions of their 
contents in respect of the amount of water absorbed during steeping in the 
solutions of acid. The endosperms of the grains steeped in 9 per cent, 
sulphuric acid were soft, and the tissues of the embryos were turgid through 
absorption of water. The endosperms of the grains steeped in 18 per cent, 
acid were not so soft, and the embryos, although distinctly moist, were 
much less so than in the experiment with weaker acid. In the case of the 
grains steeped in 36 per cent, acid, both their endosperms and embryos 
appeared to be as hard and dry as they were previous to steeping in the 
acid. 
It is evident when a semi-permeable membrane capable of separating 
water and sulphuric acid is in action some such results as those described 
are to be expected, and they suggest some interesting questions in connexion 
with osmosis which are reserved for future investigation. 
In order to obtain additional proof that solutions of sulphuric acid of 
such high concentration as 18 and 36 per cent., employed in the experiments 
just described, had not gained access to the embryos of the barley grains 
and destroyed their vitality, some of the grains which had been steeped in 
these two solutions of acid were well washed in water and subsequently 
placed under conditions favourable for germination. In a few days all were 
in vigorous growth. 
Following on the experiments with sulphuric acid which have been 
described, some experiments were made in which barley grains were steeped 
in solutions of various salts in order to ascertain if water alone passes into 
the interior of the grains under these conditions. 
5 per cent, solutions of cupric sulphate, ferrous sulphate, potassium 
chromate, silver nitrate, and potassium ferrocyanide, were employed with 
the result that no trace of any of these salts was found within the coverings 
of the grains after three days 5 steeping, although in all cases the embryos 
and endosperms of the grains were softened and distended with water. 
Experiments were also made with solutions of sodium hydrate of 
varying concentration. Solutions of 1 per cent, strength and upwards 
destroyed the coverings of the grain and ultimately disintegrated the grain 
completely. 
The coverings of the grain were, however, found to withstand the 
action of a 0.5 per cent, solution, and under these conditions, although water 
passed from the solution into the grain, sodium hydrate was excluded. 
Experiments with solutions of hydrochloric acid of normal (3-65 per 
cent.) strength also showed that this acid, like sulphuric acid, is excluded 
from the interior of the grains. 
With nitric acid, however, somewhat different results were obtained. 
When barley grains were steeped in a 1 per cent, solution of this acid it 
was found that the acid was excluded during 24 hours’ immersion, and in 
