546 



♦ KNOWLEDGE ♦ 



[JcNE 26, 1885. 



suggested, for a number of the exercises for the arm and 

 wrist require strenuous hand-gripping. But hand-opening 

 and finger-working exercises are much needed. 



Observe that lifting weights by the fingers tends to crook 

 the fingers if the work is done in the usual way, the 

 pressure being against the inside of the fingers. This may 

 be corrected by lifting weights in such a way that the 

 outsides of the fingers feel the pressure. I notice here, by 

 the way, a singular mistake in Mr. Blaikie's advice for 

 correcting the cramped state of the fingers resulting from 

 much hand-gripping work. He recommends the use of the 

 fingers in pushing, as when the body is allowed to rest on 

 the outstretched arms, the fingers pressing against a wall 

 or the floor, and pushing the body back to the erect posi- 

 tion. The muscles used in this pushing action are not the 

 muscles which oppose the gripping muscles, but are these 

 very muscles, the hand-closing not the hand-opening 

 muscles. After much work in finger-pushing in this way 

 (that is, by pressure against a flat surface) the hand tends 

 to a hooked and cramped state, not exactly the same as, 

 yet resembling, the hooked hands so often seen among 

 oarsmen. 



After all, the hand is more of a grasping instrument 

 than anything else, and we do not find many exercises 

 suitable for correcting the efiects of too much gripping 

 work. Exercises in which the fingers are forced open, as 

 in the beginning of the pushing work last considered, and 

 not subsequently called upon to resist the pressure by 

 closing towards the palm, are good by actually pressing the 

 hand into fctraightness, not by exercising any counter 

 muscles. 



Here is a simple exercise for the muscles which oppose 

 the gripping muscles : — Place the tips of the fingers under 

 a heavy book, or the nearer half of a writing-desk, then 

 work the fingers as in playing the piano, so that each 

 finger is called on in its turn to lift the weight. A very 

 little work of this kind will go a long way, showing how 

 unusual is such exercise, and how weak and unpractised 

 are the hand-opening as compared with the hand-closing 

 muscles. 



THE TEREDO AND ITS WORK. 



THE ship-worm — Teredo navalis — is a niollusk belong- 

 ing to the tubiferous bivalves, and has been from 

 time immemorial, and in all quarters of the globe, the sub- 

 ject of comment on account of its ravages in timber ex- 

 posed to its attack. There are twenty-four species of the 

 teredo, but the ship- worm is the best known of these, 

 although much is yet to be made known concerning it 

 before the information upon the subject can be said to be 

 even approximately complete. Along the Gulf Coast of 

 the United States the worm has been carefully studied by 

 the builders of railroads, and the students have been re- 

 warded more abundantly in that district than those who 

 have examined the subject elsewhere. The results of some 

 of these studies are here presented, and in these results 

 some statements will be found which will prove new and 

 of interest to the scientific world. 



" If I had a boring instrument of this sort I would make 

 a fortune," said a recent observer of the teredo. He spoke 

 truly, for such an instrument, should it exist in mechanics, 

 would revolutionise the builder's art. Yet an almost similar 

 one is in daily use under a patent from the Government. 

 The instrument is the flexible shaft-boring machine. It 

 is a spiral of steel having a steel bit at its extremity, revol- 

 ving with a jmlley shaft. The spiral is protected by being 

 run through a rubber hose, so that only the auger itself 

 visibly revolves, and the machine can be handled without 



danger. The auger bit can be turned in any direction, and 

 as it is revolving at a high rate of speed, can be easily pushed 

 through timber. The first impression the working of this 

 mechanism makes upon the uninstructed observer is lasting. 

 The Teredo navulis is a natural reproduction of this instru- 

 ment, and something more. Its long and flexible body 

 terminates in cutting shells or bits, and is inclosed, for the 

 sake of its protection, in a hose-like shell, which reaches 

 from the inferior extremity to within a very short distance 

 of what is known as the head. At that point the muscles 

 come into play and work the cutters or bit-edges, and so 

 drive into the timber, cutting as smooth and as round a 

 hole as any boring machine yet invented. Like the flexible 

 auger, it can turn itself in any direction ; but it has this, 

 advantage, it can change its course at any point, whereas 

 the auger, once entered, pushes straight ahead until the 

 hole is bored the requisite depth. An auger that could be 

 guided at an angle from its course after penetrating the 

 wood would be indeed the most wonderful boring machine 

 in the world. Such a boring machine is the teredo. 



The teredo first appears in the egg, which is round like 

 a mustard-seed, and so small that a hundred of them will 

 lie in a circle the size of such a seed. They come from a 

 whitish-looking mass just below the stomach of the adult 

 teredo, about one-fourth the distance from the head to the 

 tail, and are in number from one to three millions. These 

 egsrs are laid at the beginning of the warm season in the 

 spring, and are deposited from time to time until cold 

 weather sets in. Naturally the worm is most destructive 

 during this warm season. The eggs hatch in the water 

 and give out minute worms about the twenty-fifth of an 

 inch long, and so small in diameter as to be invisible to the 

 inexperienced observer. They swim about for a day or so 

 in the water, apparently enjoying their brief time of adoles- 

 cence, and then search for timber. They enter this by 

 boring or cutting with the shells or cutters with which 

 each is provided, and the entrance they make is so small 

 that it can scarcely be seen, especially in weather-stained 

 wood. The size of the hole is about that of the period at 

 the end of this sentence. 



The worm grows at the rate of about two inches per 

 month under favourable circumstances, and digs a hole to 

 accommodate its incrtasing size. The length of the hole is, 

 therefore, a guide to the length of the teredo ; for it 

 attaches its smaller end to the entrance of its burrow, and 

 pushes forward with the growth of its body. As it pro- 

 gresses, it deposits a coating of lime upon the sides of its 

 cell, the deposit growing thinner as the animal advances, 

 being quite thick at the entrance and merely a film near 

 the head, where is collected a whitish, watery fluid, which 

 probably contains the lime secreted for making the lining 

 of the cell, and perhaps also for repairing the wear of the 

 cutters. 



The worm continues its progress for one or one and a 

 half years, and propagates and die.--. It is said by 

 naturalists to reach the length of I'l or 12 inches; but 

 they grow much larger than this in the Gulf Coast latitude. 

 The largest one authentically observed was 23 inches long, 

 and five-eighths of an inch thick ?.t the large end. Mr. 

 J. "W. Putnam, of New Orleans, from whom much interest- 

 ing data upon this subject has been obtained, says he found 

 a hole in which a teredo had died, which was three feet 

 long and three-fourths of an inch in diameter at the 

 large end. When grown, the teredo is seen to be a 

 mucilaginous worm, attenuated in shape, extremely 

 delicate to the touch, and tapering to a very small point. 

 The anterior or large end has two bifurcations, pro- 

 vided with horny styles, which close \ip against each other 

 like shells. These cutters are attached to a pair of strong 



