For mounting minute objects, carbolic acid solution will be found a useful medium--the purest crystals of carbolic acid dissolved in just sufficient water to render them fluid. No more should be dissolved than may be wanted for the time being, as if left standing exposed to the light it changes colour. Small crustacean foraminifera, the palates of moluscs, after boiling a short time in liquid potash and well washing to remove all traces of alkali, may be preserved in carbolic acid solution. Should the specimens appear cloudy gently warm the slide over a spirit lamp. _Preserving and Killing Rotatoria with cilia in situ._--Mr. C. Rousselet’s method of preserving and mounting the Rotatoria[47] has been attended with so much success that the old difficulty attendant upon the preservation of these various beautiful forms of infusorial life has been practically overcome. The process resorted to consists of four stages, namely, narcotising, killing, fixing, and preserving. In dealing with rotifers hitherto, the difficulty has been that of successfully killing them with their rotating organs fully extended. It has been found needful to have recourse in the first instance to a narcotising agent, and one that acts slowly. The most suitable is a weak solution of the hydrochlorate of cocaine, a one per cent. solution, or even weaker. This was first proposed by Mr. Weber for keeping these active little bodies quiet while under observation. Mr. Rousselet carries this agent further; he applied it to narcotise them prior to killing, and this it does most effectually. The rotifers are seen to sink to the bottom of the live-cell, and the cilia gradually to slacken in motion, and the time for killing has arrived. This is effected by Flemming’s chromo-aceto-osmic acid. A rather weak solution must be employed--consisting of 1 per cent. solution of chromic acid, 15 parts; 2 per cent. osmic acid, 4 parts; glacial acetic acid, 1 part--which is at the same time a killing and fixing medium. The word “fixing” must not be taken to imply simply fixing, as it includes rapidly _killing_ and _hardening_ and preventing further change in the tissues of the rotifers by subsequent treatment, as mounting. The animal, therefore, must remain quietly for a few minutes, and then taken out and washed in five or six changes of distilled water, and hence transferred to the preservative fluid. All this must be effected with great care. The best preservative fluid is simply distilled water, rendered antiseptic by a trace of the fixing solution (about eight drops to an ounce of water) giving the slightest tinge of yellow to the solution. This slight tinge of colour is imparted to the rotifers, otherwise they remain transparent and unchanged, while the nervous tissue throughout the body is brought out to perfection.