14 THE MICROSCOPE. 



animalcules in a single drop of water, bearing, as we now know, no 

 further resemblance one to the other than their microscopic size ; some 

 are plants, some are animals, though which is which,is, or was, diflScult 

 to decide. Many a fierce debate has been held, many a fiery word 

 spoken on this subject ; for even natural philosophers are not devoid of 

 angry feelings. The borderline separating the animal and vegetable 

 kingdom has long been debateable ground, and the tribes in close 

 contiguity on either side have constantly, though unconsciously, shifted 

 sides, now being claimed by the animal philosophers, now by the 

 vegetarians. Now, some unmistakeable spontaneous motion being 

 discovered, they are given up to the animal world ; then their outer 

 coverings yield un-doubted evidence of starch, and they are claimed 

 as true vegetables. There is one specimen in particular, the Volvoj) 

 Globator which has changed sides so often, that could it be supposed to 

 posesss o\ir finer feelings, it must be quite ashamed of itself. For a 

 long time it was considered an unmistakeable animal, as it whirled 

 round in the water by the aid of its cilife or hair-like appendages, and 

 was described as possessing an eye, a mouth, and several stomachs. 

 There is now, how-ever, no donbt as to its vegetable character. 

 Perhaps you will say, what is the difierence between a plant and a lower 

 animal ? Well, the boundary line is faint, and somewhat uncertain, 

 and there is no one characteristic mark by which to distinguish one 

 from the other. Certainly spontaneous motion is not one ; for so 

 frequent is it among vegetables, that I really think the safest plan 

 for the young microscopist is, when he sees anything ho is quite con- 

 vinced is an animal, to at once put it down as belonging to the vegetable 

 kingdom. Perhaps the most practical test is that given by Carpenter — 

 the dependence of the animal for nutriment on organic compounds taken 

 into the interior of its body ; of the vegetable, its power of obtaining 

 its own alimentary matter from inorganic material on its exterior. At 

 any rate these are the characteristics of the animal and vegetable 

 world as a whole. For while we fixtd the simplest animals, the I'rotozoa, 

 nothing more in fact than a mass of jelly, deriving their nourishment 

 as much from other animals and plants as we do from hoof 

 or potatoes, so we find the Protophyta, the humblest class of plants, 

 drawing their support from water, carbonic acid, and ammonia 

 (inorganic compounds), and liberating oxygen and absorbing carbonic 

 acid, in the same manner as the most highly organised plants. 



The microscope has been most invaluable in investigating many 

 diseases, or blights, as they were called. Tlius it was discovered that 

 the silkworm disease (muscardine), which annually carried ofi" immense 

 numbers of silkworms, was a fungous vegetation; that that most 

 troublesome malady to which our countrj men north of the Tweed 

 are more particularly liable, and which James I. said no one but a 

 king should bo allowed to have, is caused by the burrowing of a 

 small insect (Acarus scdbwi) beneath the skin : and what is stil 

 the more important, we have within the last few years discovered the 



