cedar-oil completes the preparation, which is immediately 

 examined with the microscope. If the preparation has 

 been properly spread, nearly every field is good; there is 

 no massing of the organisms so as to mate it almost im- 

 possible to study them carefully except in a few fields; 

 on the contrary, almost every organism stands out very 

 clearly. Such a preparation, including the cleaning of the 

 cover-glass, may be placed under the microscope in less 

 than three minutes. Usually a moment's examination is 

 all that is necessary, but if one desires a longer study care 

 must be taken that the water beneath the slip does not 

 evaporate. Three or four such preparations, depending 

 upon the size of the cover-glasses, may be mounted on 

 one slide. 



As before mentioned, by far the greater number of 

 cover-glass preparations are only made for diagnosis, and 

 are then thrown away; it is, therefore, absolutely unneces- 

 sary to mount at once in Canada balsam. If, after exami- 

 nation in water, it is desired to preserve any specimen, the 

 procedure is simply as follows: Again holding the slip 

 down with the thumb nail the oil is wiped off with a 

 piece of filter-paper or a cloth moistened with xylol (a 

 bottle of which should be within reach) ; a drop of water is 

 then placed at the edge of the cover-glass, which is slipped 

 off and dried between folds of filter-paper. After com- 

 pleting the drying over the flame, the preparation is 

 mounted in balsam. The specimen being already known 

 there is, therefore, no need of examining it again until the 

 balsam becomes dry. 



A recent method of making and of staining the prepa- 

 ration upon the slide and examining at once in oil with- 

 out the intervention of a cover-glass, has some advantages 

 and it often saves time. The great advantage of this 

 method is, that four or five different preparations (made 

 exactly as are cover-glass preparations) may be made 

 upon one slide and be stained simultaneously. After wash- 

 ing and thoroughly drying the slide the preparations are 

 ready for examination upon the addition of a drop of oil. 

 Many cover-classes are thus saved, the slides, which are 

 easily cleaned with a little alcohol, being ready for further 

 use. The great disadvantage of this method is the im- 

 practicability of properly mounting permanently, if so 

 desired, any one or more of the specimens thus prepared. 

 If but one preparation is made upon a slide permanent 

 mounting is simple, but, as remarked above, the great 

 advantage of this method lies in the possibility of stain- 

 ing four or five preparations at one time. 



11 



