NOTES FOR GUIDANCE IN MAKING PERMANENT 



PREPARATIONS, 



Only very simple directions are here given, such as will 

 serve to aid students who have had no experience in preparing 

 objects for microscopic examination to make preparations when 

 this is desirable for proper laboratory study. Those who desire 

 to prepare material for serial sections, or who wish to make 

 whole mounts of delicate material, are referred to Lee's Micro- 

 tomist's Vade Mecum. Short directions for preparing forms 

 like Paramsecium are given on p. 212. 



The steps taken in preparing total mounts include: 



1. Fixing, or killing. 



2. Washing. 



3. Dehydrating and staining. 



4. Clearing. 



5. Mounting. 



Fixing. — This is necessary to keep the cells and tissues as 

 nearly as possible in their natural position, shape, and structure, 

 and in order that the protoplasm composing them may be kept 

 in condition to stain satisfactorily. 



In selecting a fixing agent remember: 



1. If the material is highly irritable and contractile, it will 

 have to be killed practically instantly with hot solutions, or 

 be previously narcotized. 



2. If there is much lime, an agent that contains much acid 

 should not be used, as the lime will be dissolved and the bubbles 

 of gas are likely to tear or distort tissues. 



3. Where rapid fixation is desirable, as in expanded hydroids 

 and the like, sublimate-acetic (hot) is preferable. Where the 

 tissue, or the animal, is not specially muscular, or liable to contrac- 

 tion, any of the fluids can be used. The time objects should 

 be left in the killing solution varies, approximately, directly as 



208 



