Now it also appears to us, that, in those casts where the clash of an oar produces a flash of pale light, without distinct sparks, or where the well-known stream of light accompanies the descent of a fishing line, these effects arise from the microscopic animals already described, and neither from any imaginary detached secretions of fishes, nor from decomposing animal matter ; because, in all such cases, the water abounds with those minuter crea tures. Though we cannot add many testimonies in sup port of our own on this subject, we shall quote the very few that have occurred to us in the course of our reading, as bearing on this part of the question. In the late voyage of Captain Tuckey, in the narratives of Riville, Newland, and Langgtaff, as well as in those of Cook, La Perouse, and Horsburgh, formerly noticed, it was remarked that great tracts of sea were sometimes found diffusedly lumi nous, shining without sparks, and with a faint general light. Some of these observers compare the effect to that which might be produced by a plain of snow ; others have thought that the sea resembled milk. By some of these persons it has further been observed, that this ap pearance was produced by myriads of minute animals. Their characters, however, have seldom been described ; and it is more than probable that many different kinds have been found, though no attention was exerted in dis criminating them. Professor Smith appears to have fallen into an error, in considering this luminous diffused mat ter as dead, or a detached substance, consisting of solid spherical particles. Such particles are indeed common ; but, instead of being dead matter, they are living animals ; belonging, as it appeared to us, sometimes to the genera Vorticella and Vol vox, and at others to genera not yet named ; to new and neglected animals, in short. It is easy to account for this error from the use of the com pound microscope, and from operating on a single drop of water ; as, by this, their motions become checked, so that they may easily be mistaken for dead inorganic par ticles.
On this account, to warn future observers against simi lar errors, and to enable others to save themselves trouble by profiting from our experience, we will not terminate this part of our subject without describing particularly the mode we followed in our attempts to draw these animals, and to discover their forms and distinctions.
They are very commonly found in milky or turbid wa ter, where they are abundant ; and on examining such water, it is found filled with floating fibres, that appear to have been produced by their own destruction after death. In the Vibrios, among which, taking this ill-contrived genus as it now stands, we have discovered about fifteen new species ; it is easy to witness the death of the animal, and its gradual dissolution, since that takes place in the course of a few minutes, or in the larger in a quarter of an hour. That opacity sometimes interferes a good deal with these observations, and is therefore better avoided, if possible. In the same way, they are more difficult to examine when numerous, as they disturb each other by their rapid movements, and prevent the observer from keeping any of them within the focus of the lens. Some
species of a genus, which has yet received no name, are so extremely troublesome in this respect, from the rapi dity of their motions, that if they happen to be present, it is almost hopeless to attempt to make any accurate ob servations.
It is preferable to examine all these animals by candle light, as ordinary daylight is not sufficient for the pur pose; nor can the light of the sun be managed in such a manner, as, at the same time, to be endured by the eye, and to serve the purpose of illuminating the objects. It is desirable to use more than one candle, as it is conveni ent to have more than one luminous spot under command, the rapid motions of these animals carrying them so quick ly out of the limits of one spot as to cause considerable trouble to the observer, who has many things to distrac' his attention at the same time. Some of them are best examined in the brightest light ; others at its borders; and very often it is necessary to examine the same object in different lights, before a just idea of its form can be ob tained. A separate light is also required to illuminate the paper on which the drawings are to be made, the eye be ing so far paralyzed by the excess of light required to view them, as not to be able to see, in a moderate degree of illumination, and it being absolutely necessary to draw them without losing the least practicable interval of time after viewing them through the lens. A few seconds are sufficient to cause the observer to forget the exact figure of the parts which he is to delineate.
The most convenient receptacle in which they can be placed for examination is a rummer, or conoidal glass, of such dimensions as to contain about half a pint. It is, in the first place, quite necessary that they should be at li berty, as it is only when in motion that many of them can at all be discovered, and as the peculiar nature of their motions, which, in all, are very different, and high ly characteristic, is of great use in discriminating indivi duals otherwise much resembling each other. It is true, that this is productive of great inconvenience, from their passing so quickly out of the field of view ; and thus it often requires a long time, and examinations patiently re peated, to ascertain the exact figure of one individual.
It is impossible to confine them in a single drop of wa ter in the usual manner, unless absolutely microscopic, and as small as the Infusoria,without losing sight of their forms. In this way they come to a state of rest, and their fins, legs, antennx, and other fine parts, become invisi ble, generally collapsing close to the body. Moreover, the affection of light produced by the contact of the ani mal with the surface or edge of the drop, or of that of the drop with the glass on which it stands, totally destroys distinct vision, and renders their forms quite unintelligi ble. A glass of less dimensions than that above-mention ed, or a wine glass, is also far less convenient than a rum mer, as the smallness of the circle, or nature of the con vexity, produces a far less useful spot of light.