Materials and Equipment 65 



and sufficiently thin to be used with anything except an oil-immersion 

 objective. No. 3 coverslips, averaging about 0.30 to 0.35 mm in thickness, 

 are used only in making covers for dry wholemounts, which are not de- 

 scribed in this book. They should never be used for any other purpose. 



Circular coverslips are available in sizes from % to % in - m diameter, 

 and the size most commonly employed is a % in. (18 mm). For class 

 purposes a Yo-in. size is much more convenient and is large enough for the 

 majority of wholemounts. Square coverslips come in the same sizes as do 

 the circular ones. The choice between circular and square depends en- 

 tirely on the preference of the mounter. Square coverslips are a trifle 

 easier to handle, but round coverslips have the advantage that one can 

 "ring" the slide if one is making fluid or dry mounts. These types of 

 mounts, however, are not described in this book, for they are unsuitable 

 for elementary students. Rectangular coverslips intended for use on 3- by 

 1-in. slides are always 22 mm across their narrowest dimension and may 

 be obtained 30, 40, or 50 mm in length. It is rarely wise to use a coverslip 

 longer than 50 mm, for insufficient space will be left on the end of the 

 slide for the application of the label. Coverslips intended for use with 

 1%-in. slides are usually 35 mm on their shortest dimension, and those 

 intended for use with 2-in. slides are generally 43 mm on their shortest 

 dimension. Coverslips for use with larger slides are almost invariably 50 

 mm long. 



Containers for Handling Objects. Objects intended for microscopic 

 examination have to go through a variety of processes, which are de- 

 scribed in the next few chapters. Either the object may be put through 

 these processes and subsequently mounted or it may be attached to a 

 slide and the slide put through the processes. In either case a special 

 container is required. Small objects are usually transferred between solu- 

 tions either with a pipette (Fig. 72) or a section lifter (Fig. 73), the 

 choice between the two depending upon the size and shape of the object. 

 Where the object will stay for only a short time in a solution, it is custom- 

 ary to employ Syracuse watch glasses (Fig. 74). These are called watch 

 glasses because they have replaced the more conventional type of watch 

 glass in laboratory technique. They have the advantage over the conven- 

 tional type of being less easy to upset, and are so shaped that they may be 

 stacked one on top of the other, both for storage and prevention of too- 

 rapid evaporation of the contained solutions. They would be far better 

 called Syracuse "dishes," but the name watch glass is still in customary 

 use. Embryological watch glasses (Fig. 75) are used less for soaking 

 objects in various solutions than for embedding objects in paraffin. They 

 are very convenient for the latter purpose. They may also be used in 

 place of Syracuse watch glasses and have the advantage that they are 

 provided with a cover that prevents evaporation of the contained solu- 



