PROCURING OBJECTS. 105 



which both the bloodvessels and nerves ramify, but do not in 

 any case enter the membrane itself. 



In order to examine the surface of mucous membranes, the 

 mucus should be washed off as gently as possible, by a small 

 stream of water or a small syringe. If the epithelium be re- 

 quired, it may be detached from the surface with a scalpel, 

 placed on a glass slide, and viewed as a transparent object, with 

 a power of 200 diameters. The mucous membrane itself may 

 be seen by reflected light while under water ; a movable dis- 

 secting microscope being brought over it. In order to obtain 

 a correct idea of the external surface, sections, both horizontal 

 and vertical, should be taken and submitted to high powers. 

 When the membrane cannot be%ell cut into thin slices, it may 

 be separated with the needles, or by slight pressure in the 

 compressorium. Where epithelium is so abundant as to form 

 a layer of cuticle, it must be removed by maceration, in order 

 to see the mucous surface. 



The arrangement of the capillaries, as seen in the injected 

 mucous membranes, is exceedingly interesting and forms a nu- 

 merous class of preparations. 



CILIARY MOVEMENT. If the roof of the mouth of a living 

 frog be scraped with the end of a scalpel, and the detached 

 mucous matter placed on a glass slide, and examined with a 

 power of 200 diameters, the epithelium cells, and the move- 

 ment of their cilia, may be well seen. The most common 

 method is, however, to cut off with a pair of fine scissors a small 

 portion of the gills (branchiae) of an oyster or mussel ; lay it on 

 a slide or on a tablet of an animalcule cage, with a drop or two 

 of the fluid from the shell. With the needle-points separate 

 the filaments from each other, and cover it lightly with a thin 

 piece of glass. The cilia may then be seen in several rows, 

 beating and lashing the water with amazing activity. If fresh 

 water be added instead of that from the shell, the movement 



