THE ACTION OF TANNIN. 145 
known to require any comment. I will merely mention that it is 
soluble to the extent of 30 volumes in 1 volume of cold water; 
but this solution soon changes into sulphuric acid by the action of 
air. If, however, the gas is passed into alcohol the quantity 
absorbed is greatly increased. If this saturated solution of the 
gas in alcohol is added to water, the gas, or the greater portion of 
it, is instantly thrown off. This alcoholic solution I have found 
most satisfactory in the observation of Infusoria. When a minute 
quantity is added to a drop of water on a slip, there is at first the 
repellent action between the alcohol and the water. ‘This being 
overcome, the gas is given off, and its effect upon infusorial life is 
at once apparent. If the solution is strong they are at once 
killed, and in most cases, if the Infusoria are ciliate, the cilia are 
rendered visible ; but if the deadly solution has been strong enough 
to be hurtful but not deadly, examination may be carried on 
satisfactorily. The Infusoria are rendered almost motionless, 
while the ciliary action may be well observed. 
If, under these conditions, the slip containing Paramecia is 
allowed to become dry, the points of attachment of the cicilia to 
the body of the animal are exceedingly well defined. Where the 
cilia have become detached they almost resemble raphides. 
I think that this reagent—sulphurous oxide in alcohol—is one 
that may prove of great use in microscopy. It is not so deadly as 
osmic acid, but it has a very marked action on Infusoria ; while it 
is by no means so dangerous, and its cost is much less. The 
solution in water possesses very powerful bleaching properties, and 
the alcoholic solution, which is perfectly stable, furnishes a ready 
means of obtaining small quantities of sulphurous acid, for bleach- 
ing or other purposes. 
I would merely add in conclusion that I consider I ought 
almost to apologise for dealing with a subject so very foreign to 
my usual microscopical pursuits. The experiments I have described 
have been carried out more as a microscopical recreation than as 
a scientific research ; but they have appeared to me, and to those 
microscopists to whom I have shown them, to be of so much 
interest, and so capable in the hands of those more conversant 
with the subject than myself of further extension, that I have been 
induced to bring them forward. 
