KIDD'S OWN JOURNAL. 



157 



of animate being are composed, and to resolve 

 them into their first elements. Numerous and 

 diverse as are these substances — bones, cartilage. I 

 sinew, nerve, muscle, hair, the teeth, the nails of ; 

 the hand, the transparent lens of the eye, — all are j 

 reducible to one kind of structure. This structure i 

 is a cell. All organic substances are made up of 

 cells. The primary organic cell is a minute, | 

 pellucid globule, invisible to the naked eye, and i 

 containing within it a smaller cell, called the j 

 nucleus, which again contains a still more minute j 

 granule, called the nucleolus, or little nucleus. 

 Even the highest animals, in the early develop- 

 meat of the embryo, are composed entirely of j 

 nucleated cells, which afterwards assume the 

 forms peculiar to the various tissues. In the 

 lowest classes of animals, their more simple bodies 

 consist almost entirely of cells of this kind. If 

 we take a minute portion of the gelatinous flesh ; 

 of a medusa or a zoophyte, and crush it between 

 two plates of glass beneath the microscope, the 

 substance is presently resolved into a multitude | 

 of oval pellucid granules, each of which for a short 

 time maintains a spontaneous motion, sometimes 

 rotating upon itself, but more commonly jerking 

 or quivering irregularly. These are the primary 

 cells, and their motion is, doubtless, to be attributed 

 to the presence of certain hairs, called cilia ; for 

 we cannot believe that it is at all connected with 

 currents in the fluid that surrounds them, to 

 which it has sometimes been referred. 



Cilia play an important part in the economy of 

 all animals. Even in the highest forms, many of 

 the internal surfaces are furnished with them, and 

 nearly all the motions which do not depend upon 

 muscular contraction are produced by them. In 

 the lower tribes, especially those which are 

 aquatic, the office of these organs becomes more 

 important and more apparent, until in the very 

 lowest we find all movement originating with them. 



The form of these essential organs is that of 

 slender, tapering hairs, commonly arranged in 

 rows, resembling the eyelashes; whence their 

 name. The base of each hair is attached to the 

 surface of the body to which it belongs, its whole 

 length besides being free. During life each 

 cilium maintains an uniform motion of a waving 

 or lashing kind, bending down in one direction, 

 and then straightening itself again. This move- 

 ment is not performed by all the cilia together or 

 in unison, but in rapid succession : for example, 

 the instant after one has begun to bend, the next 

 begins, then the next, and so on ; so that before 

 the first has resumed its erect condition, perhaps 

 half-a-dozen of its successors are in different 

 degrees of flexure. This sort of motion will 

 perhaps be better understood by referring to that 

 beautiful and familiar spectacle, the waves 

 produced by the breeze upon a field of 

 standing corn. The motion is exactly the 

 same in both cases. The wind as it sweeps 

 along, bends each stalk in turn, and each in turn 

 reassumes its erect posture; thus the wave runs 

 steadily on, though the stalks of corn never remove 

 from their place. The appearance of the ciliary 

 wave, when viewed with a good microscope, is so 

 exquisitely charming, that even those who have 

 been long familiar with it can scarcely ever 

 behold it without admiration. Let us now speak 

 of the 



INFUSORIA. 



The most minute and the most simple of all 

 living beings, so far as the powers of the best 

 microscopes have yet reached, closely resembles 

 such a ciliated cell as we have been describing. 

 It has been called the Twilight Monad (Monas 

 crepusculimi), so named because it is considered 

 to be as it were the unit of existence — the point 

 where the glimmering spark of life first emerges 

 out of the darkness of nonentity. It consists of a 

 tiny speck of pellucid matter rounded in form, 

 and supposed, from its movements and from ana- 

 logy, to be furnished with a single cilium, by 

 the lashing action of which it rows itself through 

 the water. No words can convey an adequate 

 idea of the size of an animal so minute as this, but 

 the imagination may be assisted by supposing a 

 number of them to be arranged side by side in 

 contact with each other, like the beads of a neck- 

 lace, when twelve thousand of them would go 

 comfortably within the length of a single inch. 

 Eight hundred thousand millions would be con- 

 tained in a cubic inch; and as they are found 

 swarming in water to such a degree as that each 

 is sepj. rated from its neighbors by a space not 

 greater than its own diameter, a single drop of 

 such water has been estimated to contain a thou- 

 sand millions of living active beings. If we take 

 a bunch of leaves, of the common sage for example, 

 or a few twigs of hay, and, tying them into a 

 bundle, suspend them in a jar of water, allowing 

 the contents to remain untouched, but exposed to 

 the air, some interesting results will follow. If 

 we examine it on the second day, we shall find 

 a sort of scum covering the surface, and the whole 

 fluid becoming turbid, and slightly tinged with 

 green. If now we take, with the point of a quill 

 or a pin, a minute drop of the liquid, and examine 

 it with a good microscope under a magnifying 

 power of about two hundred diameters, we discover 

 the water to be swarming with animal life. 

 Immense multitudes of minute round or oval 

 atoms are present, which move rapidly with a 

 gliding action. These are animals of the genus 

 Monas just described. Among them we shall 

 probably see other bodies still more minute, resem-. 

 bling short lines, most of which are seen to be 

 composed of more or fewer bead-like bodies, united 

 into a chain. These occasionally bend themselves, 

 wriggle nimbly, and effect a rather rapid progres- 

 sion in this manner. The scum, or transparent 

 pellicile, is found to be composed of countless 

 millions of these latter, congregated about as 

 thickly as they can lie into patches. They con- 

 stitute the genus Vibrio. Several may be seen 

 among them briskly wriggling along, which 

 resemble a little coil of spiral wire. Such forms 

 bear the generic appellation of Spirllium. 



As all infusions of vegetable or animal sub- 

 stances are found to be speedily filled with animals 

 resembling these, in great variety, though not 

 always of the same species, the circumstance has 

 been seized by naturalists to afford a name by 

 which this class of beings should be distinguished. 

 They have been therefore called Infusoria or 

 infusory animalcules ; a very extensive group, and 

 one which, in the more advanced state of our 

 knowledge, it may be found desirable to divide, 

 since it includes animals of very different grades 

 of organisation. Those of which we have spoken 



