142 SLIDES AND COVER-GLASSES. [CH, VII. 



(§ 227) and allowed to remain a day or longer. In putting them in, 

 push one in at a time and be sure that it is entirely immersed, otherwise 

 they adhere very closely, and the cleaning mixture is unable to act 

 freely. Soiled covers should be left a week or more in the cleaning 

 mixture. An indefinite sojourn in the cleaner does not seem to injure 

 the slides or covers. After one day or longer, pour off the cleaning 

 mixture into another glass jar, and rinse the cover-glasses, moving them 

 around with a gentle rotary motion. Continue the rinsing until all the 

 cleaning mixture is removed. One may rinse them occasionally, and 

 in the meantime allow a very gentle stream of water to flow on them, or 

 they may be allowed to stand quietly and have the water renewed from 

 time to time. When the cleaning mixture is removed rinse the covers 

 well with distilled water, and then cover them with 50^ to 75% alcohol. 



§223. Wiping the Cover- Glasses. — When ready to wipe the 

 cover-glasses, remove several from the alcohol and put them on a soft, 

 dry cloth, or on some of the lens paper to let them drain. Grasp a 

 cover-glass by its edges, cover the thumb and index of the other hand 

 with a soft, clean cloth or some of the lens paper. Grasp the cover be- 

 tween the thumb and index and rub the surfaces. In doing this it is 

 necessary to keep the thumb and index well opposed on directly oppo- 

 site faces of the cover so that no strain will come on it, otherwise the 

 cover is liable to be broken. 



When a cover is well wiped, hold it up and look through it toward 

 some dark object. The cover will be seen partly by transmitted and 

 partly by reflected light, and any cloudiness will be easily seen. If the 

 cover does not look clear, breathe on the faces and wipe again. If it is 

 not possible to get a cover clear in this way it should be put again into 

 the cleaning mixture. 



As the covers are wiped, put them in a clean paper box. Handle 

 them always by their edges, or use fine forceps. Do not put the fingers 

 on the faces of the covers, for that will surely cloud them. Wood-pulp 

 paper, from which most of the boxes are now made, constantly sheds 

 particles into the boxes ana thus soils the covers stored in them. This 

 can be largely obviated by coating the inside of the boxes with a thin 

 solution of shellac. 



§ 224. Cleaning Large Cover-Glasses. — For serial sections and 

 especially large sections, large quadrangular covers are used. These 

 are to be put one by one into cleaning mixture as for the smaller covers 

 and treated in every way the same. In wiping them one may proceed 

 as for the small covers, but special care is necessary to avoid breaking 

 them. A safe and good way to clean the large covers is to take two 



