14 



Journal of Applied Microscopy. 



mercury is used, add a small quantity 

 and shake the bottle until dissolved; 

 ag-ain add some and shake, and after 

 once making the solution, one will know 

 about the quantity to be used. The sec- 

 ond four-ounce bottle I fill up with three 

 ounces of water and one ounce of ammo- 

 nia. Now take a tray and place the 

 negative in it and let it soak in water for 

 about one minute; pour off the water, 

 then pour the mercury solution on the 

 negative just the same way as a devel- 

 oper; rock the tray gently as in develop- 

 ing, and watch the change in the nega- 

 tive. The background and all the dark 

 part of the negative will turn white, 

 whilst the image becomes apparent, and 

 as all the work is done by daylight, you 

 can take up the negative and hold it 

 against the light for examination. Do 

 not let the negative remain too long in 

 the solution, as you might get too great 

 intensity. Now pour the solution back 

 into its bottle, as you may use it over 

 and over until it is too weak to act, and 

 then wash the negative and tray, and 

 pour over the negative in the tray the 

 contents of bottle No. 2. The negative 

 will now turn black. The ammonia solu- 

 tion must be poured on the same as a 

 developer so as to cover quickly the 

 negative, and then rook until the nega- 

 tive Is all black, which may be seen by 

 examining it against the light from time 

 to time. Take the negative out and wash 

 in running water for about ten minutes, 

 and then dry as usual. Try it on some 

 of your weak negatives and see the effect 

 it has. 



The second dodge I use is with regard 

 to lantern-slides from photo-micro- 

 graphic negatives that lack contrast 

 somew'hat. The background of the lan- 

 tern-slide may show up somewhat mud- 

 dy on the screen. This can be remedied 

 by using a reducing agent. I make a 

 solution of potassic ferricyanide (red 

 prU'S'siate of potash) of about ten grains 

 to the ounce of water, and two or three 

 drops of this I add to about four or five 

 ounces of the ordinary hypo solution, and 

 w'ith a camel-hair brush I apply this 

 solution wherever I wish to clear up the 

 lantern-slide. By being careful not to 

 let this solution come in contact with the 

 image, you can clear the whole of the 

 background, thus making the image 

 stand out more prominently, and if some 

 of the solution gets on the image, wash 

 quickly in water and then proceed with 

 the clearing. If the lantern slide was 

 overexposed or overdeveloped, and shows 

 general fogginess, then I pour the con- 

 tents of the bottle into a small tray and 

 immerse the slide in the solution, taking 

 it out every two or three seconds, and 

 dipping into w^ater, so as to stop reduc- 

 ing. I can examine it, and if not suffi- 



ciently clear, immerse again until I 

 find the slide just what it is wanted to be. 

 If the solution becomes too weak, add 

 one or two drops more. 



As boith of these solutions are very 

 poisonous, care has to be exercised so 

 as not to introduce any into the body. 



If by these two simple suggestions I 

 have been of benefit to even one beginner 

 in photo-micrography, I will feel myself 

 amply repaid for the trouble of noting 

 them down here. 



A. M. KiRSCH, C. S. C, 

 Professor of Biology. 



University of Notre Dame, Indiana, 



Note.— In case one wants to reduce quickly 

 a part in the negative or in the lantern 

 slide, add more of the ferricyanide, say a 

 drachm to 4 drachms of hypo-solution. 



Apparatus for Removing Air from 

 Mounted Slides and Material. 



D. T. MacDougal. 



In all work upon living material with 

 the microscope, more or less inconven- 

 ience results from the adhesion of layers 

 of air to the outside surfaces, or in the 

 intercellular spaces. It is customary to 

 remove this air by placing the prepara- 

 tion under the receiver of a pump. The 

 apparatus so used, however, has been 

 designed for other purposes and is gener- 

 ally bulky and awkward. The receivers 

 ara so large that the process is slow, and 

 if a hand-power pump is used, is labo- 

 rious as well. 



The writer has examined the apparatus 

 used by Berthold in his laboratory at 

 Gottingen, which has been so useful in 

 his researches upon the structure and 

 mechanism of protoplasm, and the 

 apparatus for removing air from pre- 

 parations in the Leipsic Botanical Insti- 

 tute. The former consists of a small 

 rectangular brass receiver countersunk 

 in a table, large enough to hold a slide 

 or a small watch glass, and closed with 

 a ground-glass plate over the top. Its 

 uses are necessarily limited. The Leipsic 

 apparatus consists of an ordinary 

 receiver base connected with a filter 

 pump. The great volume of air enclosed 

 in the long connecting tubes and the 

 large receiver makes the process of ex- 

 haustion a very long one, and the 

 manipulation of the valves is so compli- 

 cated, that the director finds it necessary 

 to post a set of directions or rules of 

 manipulation, the infraction of which is 

 punishable by a stated fine of two to five 

 cents for each offense. 



The apparatus that has been found 

 most useful, in my courses in the physi- 

 ology of the cell, consists essentially of a 

 tubular metal receiver connected with a 

 filter pump by a metal tube containing a 



