224 



APPENDIX. 



[No. XIV. 



A powerful permanent magnet would answer as well as the temporary- 

 magnet; but permanent magnets are expensive, and not so constantly 

 at hand. When soft iron is impacted in any part of the hody, we do 

 not requii'e either the electro- or permanent magnet, for on this substance 

 we are unable to confer magnetic properties. 



We should never think of taking the trouble of magnetizing a part 

 suspected to contain steel, or iron, unless we could get no indication of 

 its presence without ; for, perchance, the object might be sufficiently large 

 to give indication without being magnetized, or it may have been mag- 

 netized before its introduction. 



Almost all my steel instruments, in common use, are more or less 

 magnetic, from their having been exposed to electricity whilst performing 

 my electrical experiments ; and, therefore, should I have the misfortune 

 to introduce them into my body, they would be indicated without any 

 process to render them further magnetic. Although foreign to a course 

 of lectures on surgery, I may state that, when handling powerful magnets, 

 you should always put aside your watch, for my own has many a time 

 played me most troublesome pranks from its springs having become 

 magnetic. 



To test the existence of a magnet within the body, we may take a 

 magnetized sewing-needle, and suspend it by a piece of silkworm's silk, 

 when it will exhibit certain phenomena upon the approach of the suspected 

 part, provided it contain a piece of magnetized steel. Although this 

 simple contrivance will amply suffice, I myself possess a needle which 

 was made for me by Messrs. WHlats, of Cheapside, and which is well 

 adapted for the purpose. 



It consists, as you perceive, of a delicate needle, about six inches long, 

 centred upon a small agate cup, resting upon a steel point, so that the 



smallest possible amount of resistance is 

 offered to its free play, fig. 13. 



When a part, containing magnetic steel, 

 is brought near the needle, it may be either 

 attracted or repelled ; it may move upwards 

 or downwards ; or it may exhibit disquietude 

 according to the position in which the 

 new magnet is held. We may detect the 

 position of the foreign body, when it is of 

 any size, by ascertaining where its north 

 and south poles lie; and these are deter- 

 mined by their repelling and attracting the opposite poles of the magnetic 

 needle. The disquietude, or motion upwards and downwards, merely 

 indicates magnetism, but not the direction of the magnet. 



Tou wUl doubtless be surprised when I teU you that, in this manner, 

 I have detected a piece of needle impacted in the finger of a young woman, 

 although it weighed but the seventh of a grain. This gave such 

 marked indications, that I found out tolerably well the position of its 

 north and south poles, though I could not ascertain the presence of a 

 foreign body in any other way. I tried expeiiments on smaller pieces, at 

 short distances, such as half an inch to an inch, and I found that a piece 

 of needle, weighing -^g of a grain, gave decided indications after having 



Fio. 13. Magnetized N^eedle, for dis. 

 covering needles within the hody. 



