and Laboratory Methods. ^667 



the chloroform of which dissolves the oil and at the same time hardens the 

 celloidin. After three to five minutes the slides may be carried to stains, 

 whether they be alcoholic or aqueous, without fear of losing a section. If the 

 chloroform does not act long enough the whole series will float off, after soaking 

 in water. The sections will still be held in a film of celloidin and may be res- 

 cued by floating back onto a slide, dehydrated by dropping alcohol (95 per cent.) 

 over them and finally afiixed by flowing No. 2 over them again. 



Methylen blue, fuchsin and anilin blue-black stain celloidin, hence these 

 should not be used with this affixation. 



After staining, one may carry the sections up through the alcohols to 05 per 

 cent. Absolute alcohol must be avoided unless chloroform has been added to 

 it. It has been found most advisable to clear from 95 per cent, alcohol, by 

 using cedar oil, turpentine, oil of cajeput, to which a little chloroform has been 

 added, carbol xylol, creosote, or anilin oil. Oil of cloves, pennyroyal, pepper- 

 mint and bergamot are good clearing agents, but require chloroform to keep 

 them from dissolving the affixative. After clearing, run to xylol and mount in 

 Canada balsam. 



When celloidin sections are to be mounted, they are arranged on the slide in 

 95 per cent, alcohol. After draining off the excess of 95, solution No. 2 is 

 applied freely with a camel's hair brush. When dry it is hardened in No. 3 and 

 the subsequent processes are carried out as above directed for parafiin sections. 

 Science Teacher, Little Falls High School, Little Falls, N. Y. C. W. HahN, A. M. 



A New Screen for the Projection Microscope. 



In fitting a lecture room with a projection microscope, we found that the 

 heavy curtain hung on spring rollers, that is so much used for projection pur- 

 poses, was unsatisfactory, and since a sufiiciently large area of white wall, which 

 gives the best surface for this work, was not available, we have spent some time 

 in devising a satisfactory substitute. The college janitor, Mr. Downing, has 

 constructed a screen which gives thorough satisfaction, and is, so far as I know, 

 of an entirely new design. 



Directly across the room from the lantern is a blackboard, built into the wall, 

 with chart frames sliding in grooves at either end, and so balanced that they can 

 be drawn down in front of the blackboard or pushed up over it, out of the way. 

 Another frame, eight feet square, was made and hung so as to slide exactly as 

 do the chart frames. On this was fastened, with glue and tacks, large sheets of very 

 heavy cardboard. Their edges were fitted as carefully as possible, and any spaces 

 left filled with putty, and the joints painted over with shellac. The whole was then 

 covered with several coats of white kalsomine spread very thin, and of such a 

 composition that brush marks are not noticeable. The result is a surface that is 

 almost as good as a white wall, and much better than any curtain I have ever 

 seen. When in use the screen is drawn down in front of the blackboard, and 

 later pushed up above it, entirely out of the way. 



Our lantern is a Thompson double one, the upper arranged for ordinary 

 lantern slide projection, the lower for use with the microscope. The upper Ian- 



