THE AMERICAN MONTHLY 



[Jjimiary, 



outside was indurated, and when re- 

 moved the whole seemed perfectly 

 sealed and show^ed no tendency to 

 the smearing when ^viped hard, that 

 had caused me at first to suppose 

 these mounts were spoiled, and they 

 remain up to the present moment 

 now apparently good. The boro- 

 glyceride 50 per cent, solution will 

 not permit as much chloride of tin 

 to be dissolved as I mentioned in the 

 directions for the gelatin preparation 

 ' in the September number. A 25 or 30 

 per cent, solution will be better here, 

 and this medium still answers ad- 

 mirably for ordinary diatoms. 



' The gelatin and tin compound is 

 more hygroscopic than the compound 

 of boro-glyceride and antimony ; still 

 if properly made and used will answer 

 admirably and remain unchanged, 

 I believe, for anv length of time.' 



The value of these mounting me- 

 dia is not easily over-estimated. 

 They are not yet in general use, and 

 have not been applied to many sci- 

 entific investigations. They are not 

 even in the market, and this may be 

 a hint to some of our readers who 

 may wish to make their microscop- 

 ical work a source of some profit, 

 for thei^e should be a demand for the 

 media among the dealers. There 

 can be no doubt their use w'ill be- 

 come general among those who use 

 the microscope for verv fine work ; 

 and it seems not improbable that thev 

 will be of very great value to the 

 student of bacteria, making clear the 

 more minute characters that are 

 scarcely discernible in balsam. It 

 needs but a glance at the Plenro- 

 sigjna or the lines on Amphlpleura 

 to perceive the wonderful benefit to 

 be derived from their application to 

 many researches in biology and his- 

 tology. 



o 



All Efficient Pipette. 



BY D. S. KELLICOTT. 



A pipette, or dropping tube, is a very 

 simple piece of a p p a r a t u s — one 

 scarcely worth while to write about 



and to take up the space of a scientific 

 periodical — but it is useful, if simple, 

 and when just that particular instru- 

 ment is wanted, it is indispensable — 

 ' for want of a nail,' etc. 



An elastic ball pipette, properly 

 constructed, is in every way superior 

 to the simpler dropping tube filled by 

 hydrostatic pressure, and controlled 

 by closing and opening the upper end 

 by the finger. vSuch an instrument 

 should be prompt ; should draw the 

 water up forciblv in order to catch 

 with facility minute swimming forms ; 

 it should enable the hand to deliver 

 accurately few or man}' drops, and 

 the bulb should be so firm that it 

 serves for a handle without forcing- 

 out the contents of the tube. It is 

 needless to remark that a person at 

 work needs a number of pipettes — 

 some with wide mouths, others 

 drawn out to a narrow orifice, and 

 others, perhaps, with a special bul- 

 bous reservoir blown in the tube. 

 All styles are worked equally well by 

 the arrangement which I started out 

 to describe. 



This is made from the cheap play- 

 ing balls which may be had of suita- 

 ble sizes for a few cents each. I for- 

 merly used them by enlarging the air 

 opening bv means of a heated wire to 

 fit the upper end of the glass-tube, 

 but bv use it soon got loose and worth- 

 less. To prevent the tearing out of 

 the rubber I now bore an additional 

 hole through the opposite side of the 

 ball, and pass the tube through both 

 openings ; the protruding upper end 

 is then hermetically sealed or plugged 

 by a cork. The l3all is now firmly 

 supported, and, after a hole has been 

 drilled or filed through the tube so as 

 to come within the ball, the pipette is 

 complete and it is durable. The walls 

 of the bulb are stiff so that a strong 

 suction may be had if desired, and 

 the instrument used by grasping the 

 ball without danger of dropping the 

 contents at the wrong time and place. 



The tubes require cleaning by means 

 of a little cotton on the end of a wire, 

 so those drawn to a point had better 



