Volume 1

Science for all / edited by Robert Brown.

Date:
[1877?-1882?]
Catalogue details

Licence: Public Domain Mark

Credit: Science for all / edited by Robert Brown. Source: Wellcome Collection.

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    which exists around us, there may be much on which the far-seeing glance of science rests that is dubious and uncertain. It may be shown that in many cases the common distinctions between animals and plants are utterly valueless when applied to the identification of some tolerably well- known forms of life. The whole question before us is one which has grown out of the increasing re- search of modern times; the advances of science thus resulting in the demonstration of our ignorance of many of the fields of inquiry which lie before our gaze. And in what follows we shall endeavour to show, not merely that the task of separating some animals from some plants is attended with great difficulty, but also that it may be impossible to declare, in the present state of our knowledge, what are the essential characters of the animal, and what the unmistakable features of the plant. A simple experiment in the production and development of some lower forms of life, will serve as a starting-point for our inquiries into the special characteristics of the two great groups of living beings. Some chopped hay is placed in a vessel, and through the addition of water an infusion thereof is made. This infusion is further allowed to stand freely exposed to the air for a week or so, and at the expiry of that period we place a drop of the liquid under a microscope of high power. Then a wonderful sight bursts upon our view. The fluid which the ordinary observer might have expected to be simply turbid from the presence of particles derived from the dead hay, is seen literally to swarm with life. Rushing hither and thither across the field of the microscope are numberless I specks, which our first glance assures us are living beings. When the eye has had time to become better acquainted with the scene on which it rests, it may assort or parcel out the organisms of the in- fusion into various kinds or grades. There, for instance, are minute i-od-shaped bodies which wriggle ::boat with an ill-defined,jerking motion. These are bacteria (Fig. 1). There, again, are bodies of dif- ferent form and of larger size, which appear to consist of a number of the rod-like bacteria united, end to end, and which the biologist names vibrios (Fig. 2). But we also discern bodies which are different from either of the organisms just mentioned, and a Fig, l.~Bacterium termo. Magnified 600 times (a), and 1,600 times (6). which attract attention from the rapidity of their movements, as they flit hither and thither like swift vessels, through their miniature sea. Stay; there is one of these active bodies (Fig. 3) which has come to rest for awhile, and which permits us, luckily, to obtain a better view of its form and nature. You notice it to be pear-shaped, and if you are capable of forming an idea of the size of the minute objects with which the microscopist deals, you will not be surjDrised to learn that the body you see before you measures about the three-thousandth (^ gth) part of an inch in length. This pear-shaped speck bears at its narrow end a long tail, formed of a fllament which we may compare to a miniature eyelash, and which has been named a cilium. By more careful observation we might see that a second tail, or cilium, was present, and that this latter appendage was also attached to the slender extremity of the body. The body itself presents few or no features for remark. But if we are fortimate in our selection and mani- pulation of our specimen, we shall be able to see within the body a clear round space, which ever and anon contracts itself with a jerk and disappears, only, however, to reappear with its clear surface as before. Now the creature is ofi again on its pere- grinations, to add one more unit to the hustling and jostling crowds which people the drop of water before us. You are able, as it moves, to see that the longer of the two tails, or cilise, serves as a kind of propeller, whilst the second tail extends behind; and you may sometimes observe the creature to anchor itself by the second cilium, and then spin round and round the flxed point like some cmious top of vital construction. Then it releases itself, and is off again on its wild career—jostling its friends and neighbours in the struggle for existence in which animalcule and man appear alike to participate. Such is a brief description of a sight well known to every student of the microscope, but which, despite its familiar nature, can rarely fail to evoke interest and to serve as the exciting cause of a laudable and scientific curiosity. What is this creatvu'e which is seen to be represented by its thousands in a drop of hay-infusion ? The popular idea that power of motion is the exclusive right of the animal woifld unhesitatingly declare that the creature falls under the paternal care of the zoologist. But the man of science would reply that whilst the MoTiads, as he terms these creatures, 7na^/ be animals, he sees no adequate reason, on the other hand, for refusing assent to the statement that they ma^ be plants. Let us try to examine the question somewhat in detail, and place ourselves in the position of a
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