Essays on the Microscope / Containing a Practical Description of the Most Improved Microscopes, a General History of Insects, etc., etc.

by George Adams

To view the particles of the blood, take a small drop of it when warm, and spread it as thin as possible upon a flat piece of glass. By diluting it a little with warm water, some of the larger particles will divide from the smaller, and many of them will be subdivided into still smaller; or a little drop of blood may be put into a capillary tube of glass, and be then presented before the microscope. Mr. Baker advises the mixing the blood with a little warm milk, which he says, will cause the unbroken particles to be very distinctly seen. But the most accurate observer of these particles was Mr. Hewson, and he says they have been termed globules with great impropriety, being in reality flat bodies. When we consider how many ingenious persons have been employed in examining the blood with the best microscopes, it appears surprizing that the figure of the particles should be mistaken; but the wonder is lessened when we reflect how many obvious things are overlooked, till our attention is particularly directed towards them; and besides, the blood in the human subject, and in quadrupeds, is so full of these particles, that it is with great difficulty they can be seen separate, until the blood is diluted. It was by discovering a proper method to effect this, that Mr. Hewson was indebted for his success. He diluted the particles with serum, in which they would remain undissolved, and as he could dilute them to any degree with the serum, he could easily examine the particles distinct from each other; for example, take a small quantity of the serum of the human blood, and shake a piece of crassamentum in it, till it be coloured a little with the red particles; then with a soft hair pencil spread a little of it on a piece of thin glass, and place this glass under the microscope, in such a manner as not to be quite horizontal, but rather higher at one end than the other; by which means the serum will flow from the higher to the lower extremity, and as it flows, some of the particles will be found to swim on their flat sides, and will appear to have a dark spot in the middle; others will turn over from one side to the other, as they roll down the glass.

Several authors have described an apparatus for viewing the circulation of the blood in the mesentery of a frog; but as the cruelty attendant on these kinds of investigations would deprive the humane reader of a great part of the gratification which might otherwise result from them, he will probably rest satisfied with the accounts of such experiments to be met with in authors; especially as there is an abundant variety of objects on which he may exercise his ingenuity without sacrificing the nicer feelings of humanity.[44]

[44] Whatever right mankind may claim over the lives of every creature that is placed in a subordinate rank of being to themselves, in respect of food and self-defence, as well as for the improvement of science, and their judicious and ingenious application to the various purposes of use and ornament in human life, we certainly cannot, on the principles of reason and justice, assert a privilege to gratify a wanton curiosity, or the sports of an inordinate fancy, by the exercise of an unnecessary cruelty over them. The immortal Shakspeare, in a passage which has often been quoted, says,

———the poor beetle that we tread upon
In corporal sufferance finds a pang as great
As when a giant dies.

It may, however, be doubted whether this particular instance is strictly conformable to fact; different animals certainly possess different degrees of sensibility, and some are consequently more susceptible of pain than others. It is a remarkable circumstance that the Hippobosca equina, or Horse-fly, will live, run, nay even copulate, after being deprived of its head; most flies will survive that loss for some time, and the loss of a leg or two does not prevent their appearing as lively and alert as if they had sustained no injury. Many insects, on being caught, will freely and voluntarily part with their limbs to escape; and it is well known that lobsters shed their claws. Numbers of other instances might be adduced, but on this subject it may be prudent not to enlarge.

Montaigne remarks, that there is a certain claim of kindness and benevolence which every species of creatures has a right to, from us. It is to be regretted, that this general maxim is not more attended to in the affairs of education, and pressed home upon tender minds in its full extent and latitude; the early delight which children discover in tormenting different animals should by all possible means be discouraged, as, by being unrestrained in such sports, they may at least acquire a habit of confirmed inattention to every kind of suffering but their own, if not progressively be led to the perpetration of more atrocious acts of cruelty. The supreme court of judicature at Athens thought an instance of this sort not below its cognizance, and punished a boy for putting out the eyes of a poor bird that had unhappily fallen into his hands; and the inimitable Hogarth, “the great painter of mankind,” has in his “Five Stages of Cruelty,” admirably depicted the consequences which may result from an early indulgence of a propensity towards cruelty.

In order to awaken as early as possible in the minds of children an extensive sense of humanity, it might be prudent to indulge them with a view of several sorts of insects as magnified by the microscope, and to explain to them that the same marks of divine wisdom prevail in the formation of the minutest insect, as in the most enormous leviathan; that they are equally furnished with whatever is necessary, not only for the preservation, but the happiness of their beings, in that class of existence which Providence has assigned them: in a word, that the whole construction of their respective organs distinctly and decisively, proclaims them the objects of divine benevolence, and therefore they justly ought to be so of ours. Edit.

OF ANIMALCULA IN INFUSIONS, &C.

These require little or no preparation. The first object is to procure them, the second, to render them visible by the microscope. A few observations, however, may be of use. Many drops of water may be examined before any can be found; so that if the observer be too hasty, he may be easily disappointed, though other parts of the same water may be fully peopled by them.

The surface of infused liquors is generally covered with a thin pellicle, which is easily broken, but acquires thickness by standing; the greatest number of animalcula are generally to be found in this superficial film.