ACCESSORY APPARATUS. 129 



of something less than the actual size. As the forceps, in Marine re- 

 searches, have continually to be plunged into sea- water, it is better that 

 they should bo made of brass or of German silver than of steel, since the 

 latter rusts far more readily; and as they are not intended (like Dissecting- 

 forceps) to take a firm grasp of the object, but merely to hold it, they 

 may be made very light, and their spring-portion slender. As it is es- 

 sential, however, to their utility, that their points should meet accurately, 

 it is well that one of the blades should be furnished with a guide-pin 

 passing through a hole in the other. 



The foregoing constitute, it is believed, all the most important pieces 

 of Apparatus which can be considered in the light of Accessories to the 

 Microscope. Those which have been contrived to afford facilities for the 

 preparation and mounting of Objects, will be described in a future chap- 

 ter (Chap. v.). And the simple and efficient substitute which the Author 

 has been accustomed to use for the Frog-Plate thought essential by 

 many Microscopists, will be described in Chap. XX. under the head of 

 Circulation of the Blood. 



