DISSECTING TROUGHS. 167 



carry on minute dissections, as the operation can be per- 

 formed with much more certainty than is the case in more 

 mobile fluids. 



In whatever fluid the specimen for dissection be im- 

 mersed, a trough is necessary to hold it, such as shown 

 in Fig. 152, and this may be either of guttapercha or 

 glass, not too large, but roomy enough for working, and 

 also for the disposal of loose matter. Half an inch in 

 depth is ample (except for special subjects), as if deeper, 

 the sides are apt to interfere with the free use of the 

 needles and fingers. 



If the trough is of glass, a suitable bedding may be run 

 in to a depth of a 

 quarter of an inch, to 

 which the subject can 

 be pinned down. A 

 translucent bottom 

 may be made of a 

 mixture of napthalin 



and stearine, an FIG ^ 



opaque bedding of 



equal parts of resin and beeswax, thinned to the neces- 

 sary consistency with unsalted lard, and coloured black 

 with lamp-black, or white with oxide of zinc or dried 

 china-clay. 



While dissecting, no instruments are more handy than 

 ordinary sewing needles, thrust with the eye first into 

 cedar-wood handles. They may be bent to any required 

 shape while heated in the gas or a spirit-lamp flame, 

 and afterwards rehardened by heating and. plunging, while 

 hot, into oil. They must be kept well polished, as if any 

 roughness prevail on their surface it is next to impossible 

 to produce anything but torn and disfigured dissections. 



Camel-hair pencils are indispensable agents for the 



