Journal of Applied Microscopy. 497 



A Differential Stain for Goblet Cells in the Small Intestine. 



The small intestine of the cat injected with the ordinary gelatin injection mass, 

 hardened in 70 per cent, alcohol and imbedded in celloidin in the usual way, 

 was cut in sections seven to fifteen microns in thickness. The sections were 

 first stained in Mayer's hajmatein fifteen to thirty minutes, washed in 70 per 

 cent, alcohol, then stained separately on the slide in a solution of Bismark 

 brown in 70 per cent, alcohol for a very short time. The mucus-containing 

 goblet-cells are stained brilliantly with the Bismark brown ; all other cells show 

 the characteristic haematein stain. The contrast between the two colors makes 

 this the best of several processes we have tried for this purpose. 

 Biological Laboratory, University of Missouri. CharLES ThOM. 



A Test of Focal Depth. 



In connection with some experimental work in the physical laboratory it was 

 suggested to me to make some measurements of focal depth. If an object on 

 the stage of a microscope is brought into focus, there is for every combination 

 of eye-piece and objective a certain range through which the tube may be 

 elevated or depressed, and during which the clearness of focus seems to undergo 

 no change. To determine the upper and lower limits of this position affords an 

 admirable experiment for practice in accurate settings, and I have collected some 

 of my results into tabular form, thinking that they might be of interest to reader^ 

 of the Journal. 



The microscope used v,^as a Bausch & Lomb instrument of the old type. The 

 pitch of the slow-motion screw was 1-80 inch, and the head was divided into 

 twenty-five divisions, and these divisions, when reading, into fifths ; so that 

 motion through one division represented 1-2000 inch, and through one subdi- 

 vision 1-10000 inch. The specimen chosen for observation was a section of an 

 ivy leaf. Eye-pieces A, B, and C were in turn used, with objectives of one, one- 

 half, one-third, one-fourth, one-sixth, one-tenth, and one-twelfth inch. The last 

 two did not show sufficient depth to yield a series of uniform readings. 



In the tables which follow are noted the combination of eye-piece and 

 objective used — ten results in each case, expressed in terms of scale divisions — 

 and finally the focal depth resulting from the mean of these readings. 



ONE-INCH OBJECTIVE. ONE-HALF INCH OBJECTIVE. 



