THE EXAMINATION AND PRESERVATION OF INFUSORIA. 9 
A small portion of leaf, with the organism upon it, may be com- 
fortably examined on a glass slip and covered with a thin film of 
talc, but for most of these organisms the immersion lenses seem 
preferable when high powers are required. 
When the organisms are found on ALyriophyllum or Anacharis 
they cannot be better exhibited than by taking a single leaf, placing 
it on a slip of glass, provided with a ledge, with a little water, cut- 
ting off every portion of the leaf which might interfere with the 
examination, and then covering with thin glass or talc. In this 
way they can be viewed with high powers, and beautifully illumi- 
nated with either spot-lens, paraboloid, or Webster's condenser. 
In any investigations, where it is desired to retain the same 
organism for any length of time, a moist chamber must be impro- 
vised, such as that constructed by Messrs. Dallinger and Drysdale, 
in their experiments on the Life History of Monads, and figured in 
the Monthly Microscopical Journal for March, 1874. 
Another moist chamber which has the merit of simplicity is 
Weber’s convex cell. This consists of a glass slide 3 inches x 1 
inch, in which is ground a shallow well having a convex lower 
surface. The organisms contained in a drop or two of water are 
to be placed in the centre of the cell, and covered over with a thin 
covering glass, afterwards being ringed with oil, brown varnish, or 
any other substance of a similar nature. Evaporation is hereby 
prevented, and if care has been taken to place the organisms upon 
the extreme summit of the convexity, they may be examined with 
the highest powers. 
During the observation of many of the Infusoria, some tissues 
and appendages are unseen, on account of their transparency or 
rapid motion ; errors of observation induced by this latter cause 
may generally be obviated by killing the organism with osmic acid, 
and the former by adding a solution of some colouring matter, of 
which methyl green, Bismark brown, carmine, picric acid, and 
magenta are the most useful. Iodide of potassium solution, 
saturated with iodine, is also very generally applicable. Osmic 
acid is usually applied in a one or two per cent. solution, and the 
best method of using it, is to place a drop of this upon the under- 
side of the cover glass before lowering it upon the slide where the 
organisms have been placed. 
As to the preservation of Infusoria, many methods have been 
devised, which have not stood the test of time. Mr. Saville Kent 
states, in Part I. of his Manual, that they may be sealed up after 
treatment with osmic acid without the addition of any other 
preservative, and that it will be found, the smaller and most 
delicate flagelliferous species are equally amenable to this treat- 
ment, preserving their flagella, and even in the case of the Choana- 
Flagellata, their sarcode collars in a life-like form, 
