It is also very proper to dry some of them, and place them between talcs in a slider; this, however requires some dexterity and a little practice; though, when executed with success, it fully rewards the pains of the observer. Choose a proper polype, and put it into a small concave lens, with a drop of water; when it is extended, and the tail fixed, pour off a little of the water, and then plunge it with the concave into some spirit of wine contained in the bowl of a large spoon; by this it is instantly killed, the arms and body contracting more or less; rub it gently while in the spirit with a small hair pencil, to cleanse it from the lice.
The difficulty now begins; for the parts of the polype, on being taken out of the spirit, immediately cling together, so that it is not practicable to extend the body, and separate the arms on the talc, without tearing them to pieces; therefore the only method is, to adjust them upon the talc while in the spirit: this may be done by slipping the talc under the body of the polype, while it lies in the spirit, and displaying its arms thereon by the small hair pencil and a pair of nippers; then lift the talc, with the polype upon it, out of the spirit; take hold of it with the nippers in the left hand, dip the pencil in the spirit with the right hand, and therewith dispose of the several parts, that they may lie in a convenient manner, at the same time brushing away any lice that may be seen upon the talc; now let it dry, which it does in a little time, and place the talc carefully in the hole of the slider. To prevent the upper talc and ring pressing on the polype, you must cut three pieces of cork, about the bigness of a pin’s head, and the depth of the polype, and fix them by gum in a triangular position, partly on the edges of the said talc, and partly to the sides of the ivory hole itself; the upper talc may then be laid on these corks, and pressed down by the ring as usual.[45]
[45] Baker on the Polypes.
OF VEGETABLES.
It were to be wished a satisfactory account could here be given of all the preparations which are requisite to fit for the microscope the objects of the vegetable kingdom. Dr. Hill is the only writer who has handled this subject. I shall, therefore, extract from his “Treatise on the Construction of Timber,” what he has said; this, together with the improvements I have made on the cutting engine, will enable the reader to pursue the subject and extend it further, both for his own pleasure, and the advantage of the public.
THE MANNER OF OBTAINING THE PARTS OF A SHOOT SEPARATE.
In the beginning of April, take a quantity of young branches from the scarlet oak, and other trees. These are first cut into lengths, of the growth of different seasons; and then part is left entire, part split, and the rest quartered. In this state they are put into a wicker basket, with large openings, or of loose work, and a heavy stone is put in with them; a rope is tied to the handle of the basket, and it is thrown into a brook of running water: at times it is taken up, and exposed a little to the air; it is frequently shook about under water, to wash off filth; and once in ten days the sticks are examined.
By degrees the parts loosen from one another, and by gentle rubbing in a bason of water just warmed, they will be so far separated, that a pencil brush will perfect the business, and afford pieces of various sizes, pure, distinct, and clean. One part will in this way separate at one time, and another, at another; but by turning the sticks to the water, and repeating the operation, in the course of four or five weeks every part may be obtained distinct. They are best examined immediately; but if any one wish to preserve them for repeated inquiries, it may be done in this manner: dissolve half an ounce of alum in two quarts of water; drop the pieces thus separated, for a few moments, into this solution, then dry them upon paper, and put them up in vials of spirit of wine, no other fluid being so well adapted to preserve these tender bodies.
TO PREPARE THE RIND FOR OBSERVATION.
As the vessels of the rind are of different diameters in various trees, though their construction and that of the blebs is perfectly the same in all, it will be best to choose for this purpose the rind of a tree wherein they are largest. The rind of the ash-leaved maple is finely suited. A piece of this may be obtained of two inches long, and will very successfully answer the intention. Such a piece being prepared without alum or spirit, but dried from the water in which it had been macerated, it is to be impregnated with lead in the following manner, to shew the apertures by their colour.