ANATOMICAL TECHNIQUE 46 



Europe, but these are now made in good variety and of excellen 

 quality by the Cramer Dry Plate Company, of St. Louis, Missour 

 All the types of plates described above may be purchased from th 

 Cramer Company. Since ordinary photographic supply house 

 often do not carry in stock the special plates needed for photc 

 micrographic and other scientific purposes, the Cramer Compan 

 undertakes to furnish these direct from its factory in St. Louis. 



The making of lantern slides is an activity which may often b 

 pursued profitably in larger botanical establishments in univei 

 sities. The most convenient method of making such slides is b 

 placing the lantern plate directly behind a negative of suitabl 

 size, namely, 3! by 4^ inches. A few seconds' exposure to a ligr 

 sheltered by ground glass in the dark room (the time dependin 

 on the character of the negative) suffices. Development of lai 

 tern slides is effected by means of a special developer to be mei 

 tioned in a subsequent paragraph. The slides must be covere 

 with a mask which can be made by cutting out black paper b 

 means of a wheel paper-cutter and appropriate metal forms, obtaii 

 able at photographic supply stores. Masks may also be purchase 

 with the various forms and sizes of opening necessitated by tl 

 different kinds of pictures. After the mask is applied the lantei 

 slide is protected by a thin cover-glass held in position by blac 

 paper binding strips which may be procured in any photograph 

 establishment. American and Continental European lantern slidi 

 are 3! by 4 inches in dimension. The English slide is 3^ inchi 

 square. The storing of lantern slides is always a problem whe 

 their number becomes large, and many filing cabinets for this pu 

 pose are on the market. The essential thing, however, is to ha~\ 

 numbers on the slides and a catalogue, so that they can readi] 

 be selected for use and easily returned to their places. The con 

 plexity of the catalogue will of course depend upon the tastes an 

 needs of the individual and the extent of his budget. 



The development of the various plates described in the for 

 going paragraph is effected by reagents which reduce to metall 

 silver the parts of the plate exposed to the light. Developers a; 

 legion, but two or three seem to answer every practical purpos 

 For making negatives pyrogallol developer is on the whole mo 



