146 



MOUNTING AND LABELING. 



[CM. VII. 



covered. It may be used several times. It acts more rapidly than the 

 dichromate mixture, but on account of the fumes is not so well adapted 

 for general laboratories. 



MOUNTING, AND PERMANENT PREPARATION OF MICROSCOPICAL 



OBJECTS. 



§ 228. Mounting a Microscopical Object is so arranging it upon 

 some suitable support (glass slide) and in some suitable mounting me- 

 dium that it may be satisfactorily studied with the microscope. 



The cover-glass on a pennanent preparation should always be consider- 

 ably larger than the object ; and where several objects are put under one 

 cover-glass it is false economy to crowd them too closely together. 



§ 229. Temporary Mounting. — For the study of living objects, like 

 amoebae, white blood corpuscles, and many other objects both animal 

 and vegetable, their living phenomena can best be studied by mounting 

 them in the natural medium. That is, for amoebae, in the water in 

 which they are found ; for the white blood corpuscles, a drop of blood 

 is used and, as the blood soon coagulates, they are in the serum. Some- 

 times it is not easy or convenient to get the natural medium, then some 

 liquid that has been found to serve in place of the natural medium is 

 used. For many things, water with a little common salt (water 100 cc. , 

 common salt yVths gram) is employed. This is the so-called normal 

 salt or saline solution. For the ciliated cells from frogs and other am- 

 phibia, nothing has been found so good as human spittle. Whatever 

 is used, the object is put on the middle of the slide and a drop of the 

 mounting medium added, and then the cover-glass. The cover is best 

 put 011 with fine forceps, as shown in Fig. 123. After 

 the cover is in place, if the preparation is to be studied 

 for some time, it is better to avoid currents and evapora- 

 tion b\' painting a ring of castor oil around the cover in 

 such a way that part of the ring will be on the slide 

 and part on the cover (Fig. 140). 



Fig. 123. To show the method of putting a cover-glass upon a 

 microscopic preparation. The cover is grasped by one edge, the 

 opposite edge is then brought down to the slide, and the cover 

 gradually lowered upon the object. 



Fig. 124. Needle Holder {Queen & Co.). By means of the 

 screw clamp or chuck at one end, the needle may be quickly 

 changed. 



Fig. 123. 



