68 



THE ART OF MAKING MICROSCOPE SLIDES 



Gray's method 



tion has proceeded this far, the sUde is 

 gently flooded with 70% alcohol The 

 correct point at which to do this is easily 

 recognizable with practice but is difficult 

 to describe in words other than the above. 

 If evaporation be allowed to proceed too 

 far, the animal, especially if it be spherical, 

 is liable to become distorted; if it be ar- 

 rested too soon, the animal is liable to be- 

 come detached. A Uttle practice will, how- 

 ever, readily allow one to determine the 

 exact moment at which the alcohol must 

 be added. 



After the alcohol has been added to the 

 shde and left for a few moments, a small 

 circle is cut around the object with a writ- 

 ing diamond, as, once lost from the field of 

 the dissecting microscope, such objects 

 as small protozoans are almost impossible 

 to distinguish from specks of dust acquired 

 in the fixing process. The slide is then 



transferred to a coplin jar of 70% alcohol, 

 for the specimen is firmly fixed in position 

 and will not be detached through any sub- 

 sequent process of staining and mounting. 



Staining may be carried out by any 

 method. It is customary to stain most 

 small fresh-water animals in alum hema- 

 toxyhn, most small fresh-water plants in 

 some safranin solution, while the writer 

 prefers, for gastrotrichans, one of the alum 

 carmines which must be allowed to act 

 over a long period. 



It is possible with the aid of this method 

 to mount 20 or 30 selected forms from a 

 collection of fresh-water plankton in less 

 than half an hour, and it will be found 

 very useful to be able to examine a collec- 

 tion of fresh-water plankton with the as- 

 surance that any unknown form may be 

 permanently attached to a shde for subse- 

 quent identification. 



