204 



♦ KNOWLEDGE ♦ 



[August 1, 1889. 



the habit of avoiding the footstalk, unless the leaf, by narrow- 

 ing down to it, makes things more even. Also pine leaves, 

 consisting of two needle like blades, joined to a common 

 base, were almost invariably drawn in by that base. Mr. 

 Darwin observed many worms by a dim liglit actually 

 dragging these and other leaves into their buirows, and he 

 remarks, " It appeared to my son and myself as if the 

 worms instantly perceived as soon as they had seized a leaf 

 in the proper manner." And I have examined a good 

 many split seed capsules of the laburnum, which the worms 

 seem very fond of; and they were almost always drawn in 

 by the tip and not by the base. Now, as worms are not 

 guided by special instincts in each case, though possessing a 

 general instinct to plug up their burrows, and as chance is 

 excluded, the most probable conclusion is that they try a 

 variety of ways of drawing an object into their burrows, 

 and at length succeed in some one way to which they stick. 

 But it is ratlier putting the cart before the horse to tell you 

 of the lining of the burrows, when I have said hardly a 

 word about the mode of making these burrows. This is 

 done in two ways, partly by the anterior end of the worm 

 acting as a wedge, and so pushing the earth away on all 

 sides, and partly by the worm actually swallowing the 

 earth. The two modes of action seem to be chosen with 

 regard to the chai-acter of the earth in which the worm is 

 burrowing. For instance, in loose garden soil, they were 

 observed many times in the act of making their burrows ; 

 but they appeared to swallow little if any of the soil. 

 Again, in tine sand which had been pressed down and well 

 watered, they swallowed a large quantity. Earth-worms 

 undoubtedly do swallow a good deal of earth — especially 

 the dark vegetable mould — for food, and it is only on this 

 plea that we can explain the multitudes of castings you 

 can see each morning, which are quite inexplicable if we 

 suppose these are only thrown up like piles of bricks and 

 mortar, when the inhabitant is enlarging his house or build- 

 ing a new one. As a rule the burrows are not deep, but in 

 cold weather, as well as in cold countries such as Scotland 

 and Scandinavia, they have been noticed to run down for 

 7 or 8 feet, and Mr. Darwin says that in England he has fre- 

 quently known them extending downwards for 3 or 4 feet. 

 They are generally lined by a layer of dark and fine earth 

 which has passed through the worm's body, they generally 

 run straight down, and are rarely branched. When you 

 louk at an earth-worm's burrow, you would think it certainly 

 never could turn round inside. But it must do so, for the 

 excretion of the earth or casting is done with its tail first 

 on one side and then on the other, and the tail is used 

 almost like a trowel, while the mouth catches hold of leaves. 

 These castings vary greatly in size : some of the largest 

 ever measured were 6 inches high .and 1^ inches thick. 

 There are two methods of estimating the quantity of earth 

 brought to the surface in any given time : one by the rate 

 at which objects left on the surface are buried ; another, a 

 still more accurate way, by weighing the quantity brought 

 up within a given period. Let ua take an example. Sir. 

 Darwin in his book on earth-worms (from which a good 

 deal of the information in this paper has been gathered) 

 states that a piece of waste swampy land near to his house 

 was enclosed, drained, ploughed, harrowed, and thickly 

 covered with burnt marl and cinders in the year 1822. 

 It was sown with grass-seed, and now supports a fair but 

 coar.se pasture. Fifteen years after, i.e. in 1837, holes were 

 dug in this land. It was found that the turf was i inch 

 thick, beneath which was a layer of vegetable mould 

 2 i inches in thickness. It was quite free from any fragments 

 of any kind, but beneath it again was a layer of mould 

 1,^ inches thick, full of bits of burnt marl, conspicuous 

 from their red colour, and coal cinders. Below this layer, 



and at a depth of 4^^ inches from the surface, was the 

 original black peaty soil with some quartz pebbles in it. 

 Thus in only fifteen years a layer of tine vegetable mould 

 2.\ inches thick had covered the land. Now as to the 

 weight of the castings. When kept in cunfinement, it has 

 been found that they only gave out eight grains daily. But 

 when you weigh separate castings obbiined out of doors, 

 some actually weigh over an ounce each. Olf a small piece 

 of turf about 22 feet square, I have collected at one sweep 

 nearly two pounds of castings. In England the largest 

 castings are found in the poorest land, as though the worms 

 had to swallow more earth to get the same amount of 

 nourishment from it. 



OUR MICROSCOPIC FOES. 



OUR DEFENCES. 

 Br A. WiNKELUiED Williams. 

 N guarding ourselves against an enemy we 

 should always keep three things in mind : 

 how to act on the defensive .again.st attacks by 

 the foe ; how to act on the offensive, and 

 destroy or disable the foe ; and how, should 

 defeat be overshadowing us, to take advantage 

 of the better part of valour, and run away. 

 So in the Bacterio Human war must we be ready with an 

 effective combination of the above three actions in order 

 that the victory may be ours. When all the forces of our 

 bodies are acting in unity — that is to .say, when we are in 

 our natural condition of perfect health — we are practically 

 invulnerable against the foes' attack, unless it be made by 

 an abnormally great multitude. We are naturally encased 

 in a suit of armour wondrously and perfectly made. A 

 layer, or series of layers, of epithelial cells covers every sur- 

 face of the body ; these cells are carefully cemented together 

 by a small amount of interstitial matter. The armour varies 

 in structure according to the requirements of the different 

 surfaces which it covers and the functions these surfaces 

 perform. The beautiful manner in which the structure 

 is adapted to the function is well seen by examining the 

 epithelium covering the skin and the respiratory surfaces. 



The function of the skin epithelium, exposed as it is to 

 great friction and to bacteria innumerable, is mainly protec- 

 tive. It consists of many layers. The cells in the lower of 

 these layers are formed of soft protoplasm, and are con- 

 tinually multiplying. As they grow older they become 

 flattened and horny, until on the surface we find scales of 

 horny keratin ; these are continually being rubbed off. The 

 skin, however, has also .another function, i.e., the secretion 

 of sweat. Accordingly we find the epithelium altered in 

 places so as to form sweat glands ; these consist of tubes of 

 a delicate epithelium. This delicate epithelium is protected 

 by a very fine and comparatively long and tortuous duct 

 leading to the surface. 



In the respii-atory passages we find other forms of 

 epithelium. In the pharynx and larynx we have a 

 stratified .squamous epithelium resembling the skin sui'- 

 face ; below this we have a far more delicate and beautiful 

 arrangement. The windpipe divides into the two main 

 bronchial tubes ; these subdivide over and over again and 

 finally end in narrow passages, around which are clustered 

 a number of minute vesicles j ust visible to the naked eye. 

 These passages, excepting the terminal ones, are lined by a 

 stratified ciliated epithelium, which is modified here and 

 there into mucous glands and mucous cells. The surface 

 cells are the largest, and are provided with many minute 

 cilia. These cilia are continually moving in such a manner 



