144 THE MICROSCOPICAL NEWS. 
strong, as the rhythmical contraction and expansion of the con- 
tractile vesicles may be still observed. In the most successful 
observations it is probable that the tannin solution has been of 
sufficient strength to act upon the very delicate cilia, and, as it 
were, to paralyse them ; while it has not been of sufficient strength 
to kill the animal outright. In the face of the accepted theory 
that ciliary motion is involuntary, it would be incorrect to say that 
the tannin acts upon the cilia in such a manner as to render them 
beyond the animal’s control ; but the cilia are certainly rendered 
inert, while the functions of the animal are but little impaired for 
a time. 
The form of tannin which I have found most convenient to use 
is the glycerole of tannin, which is merely tannin dissolved in 
glycerine in the proportions of one part to four. It is a thick, 
viscid body, very stable, easily miscible with water, and conse- 
quently very manageable, as the quantity added to the water under 
examination can be well adjusted, and the action is more satisfac- 
tory than it would be if a solution of nearly the same specific 
gravity as water were used. ‘Tannin in alcohol is not advisable on 
account principally of the repellent action between the alcohol and 
the water. 
That the immediate action of the tannin in moderate quantity 
is not to kill the Paramecium is, 1 think, apparent from the fact 
that Infusoria much more minute than Paramecia seem to be 
little affected by it. I have constantly seen these become entangled 
in the cilia of Paramecium that had been rendered motionless by. 
tannin, and extricate themselves after a time apparently little 
affected by it. But such Infusoria have not possessed cilia of the 
same character as Paramecium. On Stylonychia the tannin does 
not appear to have so decided an action, and whenever the cilia 
take the form of seta the Infusoria seem much more capable of 
resisting its paralysing action, the peculiar jerky motion of the 
sete being kept up for some time. 
I have made the remark that I think no correct ideas have 
hitherto been held as to the size and quantity of the. cilia; at 
any rate I have never seen any drawing, or read any description of 
Paramecium, as it is observed after the treatment by tannin, 
That the appearances observed are really cilia may be easily 
verified by the action of osmic acid, which kills the Paramedaum 
at once, and renders the cilia visible, but not to the extent that 
they are so rendered by the tannin. 
I may also make allusion to the action of another chemical body 
on Infusoria, and to the advantages it seems to possess in 
microscopical research. ‘This body is sulphurous acid, or, in the 
form in which I have found it most useful, solution of sulphurous 
oxide in alcohol. The properties of sulphurous oxide are too well 
