lenses may be moistened by breathing upon them; if this is not 

 sufficient, consult the instructor. 



7. Keep both eyes open, using either the right or the left. The 

 strain of microscopic work on the eyes is usually due to the 

 fatigue of constantly closing one eye. If you cannot see the object 

 with both eyes open use the eye-shade provided for that purpose. 



8. Never leave the laboratory without first placing the micro- 

 scope in its case and locking it and all your apparatus in your 

 locker. 



II. PREPARING OBJECTS. 



The preparation of objects for examination under the microscope 

 is termed mounting. Objects are usually mounted on pieces of 

 glass 3 x i in., known as slides. Observe the following directions: 



1. If the object to be studied is a mass of cells, separate it into 

 very small pieces by means of teasing needles; if it is a fluid use 

 only a very small drop. If too much fluid has been used it will run 

 out from under the cover glass and the excess must then be soaked 

 up with filter paper. Temporary preparations ure usually mounted 

 in water, permanent ones in balsam. 



2. The lenses of the microscope, the upper side of the cover 

 glass and the lower surface of the slide m^st be perfectly clean 

 and dry. 



r 



3. Having placed the object in a small drop of mounting fluid 

 take a cover glass in your left hand, rest me edge of the cover 

 on the slide near the drop and support the opposite edge on a 

 teasing needle ; lower the cover glass gradually over the drop, being 

 careful to inclose no air bubbles. Do not press upon the cover glass. 



4. Before putting a permanent preparation away label it care- 

 fully w 7 ith the name of the object and the method of preparation. 



5. Never use reagents hap-hazard but only when you have a 

 definite purpose in view. Reagents are used for fixing, hardening 

 preserving, staining, dehydrating, clearing, embedding and mount- 

 ing. Firing is the process of killing and hardening the living thing 

 so that it preserves as nearly as possible its natural form. Staining 

 is the dyeing of the object so that some parts are more deeply 

 colored than others. Dehydrating is the process of removing the 

 water from the object, usually by alcohol. Clearing usually consists 

 in substituting some oil for the alcohol which is in the object. 

 Embedding is the process of permeating and surrounding the ob- 

 ject with some substance such as paraffin, preparatory to cutting 

 sections of it. 



