112 The Preparation of Microscope Slides 



and at the same time cements it to the coverslip through the coagulation 

 of the egg white. Then transfer the coverslip to any standard fixative solu- 

 tion for a few minutes before washing and storing in alcohol. 



Coelenterata. Hydroids are usually narcotized with menthol, although 

 the author prefers his own mixture for the purpose. They are best fixed 

 in a hot mercuric-acetic mixture. 



Platyhelminthes. Some of the smaller fresh- water Turbellaria (e.g., 

 Vortex, Microstomum) may be narcotized satisfactorily by adding small 

 quantities of 2 per cent chloral hydrate to the water in which they are 

 swimming. Another good technique is to isolate the forms in a watch 

 glass of water and place the watch glass under a bell jar together with a 

 small beaker of ether. The ether vapor dissolves in the water and 

 narcotizes these forms excellently. A detailed account of the method 

 of handling the liver fluke is given in Example 4 and may be employed 

 satisfactorily for other parasitic flatworms. 



Annelida. Small, marine, free-living Polychaeta make excellent whole- 

 mounts and do not usually require narcotization before killing. They 

 should, however, be stranded on a slide, and a small quantity of the fixa- 

 tive should be dropped on them, so that they die in the flat condition 

 that makes subsequent mounting possible. Much more realistic mounts 

 are obtained by this means than if the animals are laboriously straight- 

 ened before fixing, because they usually contract into the sinuous wave 

 that they show when swimming. There seems to be no certain method 

 of fixing the Nereids with their jaws protruding. 



Fresh-water OligocJiaetes. These are best narcotized with chloroform, 

 either by adding small quantities of a saturated solution of chloroform in 

 water, or by placing them in a small quantity of water under a bell jar in 

 which an atmosphere of chloroform vapor is maintained. Leeches are 

 rather difficult to handle, and the author has had greatest success by 

 placing them in a large quantity of water to which is added, from time 

 to time, small quantities of a solution of magnesium sulfate. As soon as 

 the leeches have fallen to the bottom, much larger quantities of magne- 

 sium sulfate can be added, which will leave the leeches, in a short time, 

 in a perfectly relaxed but not expanded condition. Then they should be 

 flattened between two slides and fixed in Zenker's fluid. After the speci- 

 mens have been fixed sufficiently long to hold their shape when the glass 

 plates are removed, they are transferred for a couple of days to fresh 

 fixative and then washed in running water overnight. 



Bryozoa. Marine Bryozoa may be narcotized without the least difficulty 

 by sprinkling menthol on the surface of the water containing them. 

 Subsequent fixation is best in some chrome-acetic mixture. It is usually 

 recommended that fresh-water Bryozoa be narcotized in a cocaine solu- 

 tion, but the author has found menthol just as good and very much 



