726 SUMMARY OF CURRENT RESEARCHES RELATING TO 



those given by white light. Blue light is less to be recommended, 

 and red is altogether to be rejected. 



M. Flesch* points out the disadvantage of green glass for light 

 modifiers, as it absorbs the red rays almost completely, so that the 

 colouring in carmine preparations is not visible, and that of other 

 parts of the objects becomes indistinct. 



Photo-Micrography,']' — Professor C. H. Eain doubts "whether 

 microscopists in general are fully aware of the extent to which late 

 improvements in dry-plate photography have simplified the work. 

 To the investigating microscopist it is almost absolutely essential 

 to be able to permanently preserve the results of his observations. 

 This is usually done by the aid of the camera lucida, and the 

 zealous worker will often sit for hours with his eye fixed at the 

 instrument laboriously striving to represent an object, and if he is 

 not well skilled in the use of the pencil his labour is frequently 

 almost useless, so inaccurate is the result. By far the greater part 

 of this labour may be saved, at an expense so trifling, and with 

 results so satisfactory, that he thinks the time is at hand when every 

 working microscopist will regard a dry-plate photographic outfit as 

 a necessary part of his equipment. 



" The wet-plate process is cumbersome, and not well adapted to 

 the wants of the microscopist, bat the dry plates now in the market 

 are admirable, not only for their great sensitiveness and beautiful 

 results, but also for the ease with which they can be manipulated. 

 They can be purchased so cheaply, that it can scarcely pay the 

 microscopist to prepare them himself. Some of the great advan- 

 tages which they possess are the following : — 



" 1. They can be kept for any length of time and used as occasion 

 requires. 



" 2. If not convenient to develope the plate at the time the 

 exposure is made, it can be put away and developed at leisure even 

 after an interval of weeks. 



" 3. No dangerously poisonous chemicals are necessary in the 

 developing process. 



" 4. They are so sensitive that the light of an ordinary kerosene 

 lamp (preferably a student lamp) is amply sufficient to photograph 

 objects with all powers not higher than t^-inch objectives." Pro- 

 bably a ^-inch objective could be used by properly arranging a 

 system of condensers. 



The author adds : " As some who desire to experiment in this 

 line may require a starting-point as regards the matter of exposure, 

 I would say that with the light of a student lamp, and using a single 

 condenser, I have found that from 1^ to 2^ minutes with a 2-inch, 

 2^ to 5 with a 1-inch, and 4 to 7 minutes with a ^-inch objective are 

 about the proper times when the A eye-piece is in and using what 

 are known as Carbutt's rapid (B) plates, No. 468. When the eye- 



* SB. Phys.-Med. Gesell. Wiirzburg, 1882 (sep. repr.). 

 f Amer. Mon. Micr. Journ., iii. (1882) pp. 71-2. 



