1884.] 



MICROSCOPICAL JOURNAL. 



119 



of its convex edges ; and that, instead of 

 being central, the hght was very oblique. 

 I have not tried this iliiiniination with 

 lamp-light, but think it would succeed, 

 provided the edge of the slide have the 

 right curve. 1 send a diagram which will, 

 I think, illustrate the manner in which the 

 light is reflected. 



Possibly a prism might be made to con- 

 nect by immersion contact with the lower 

 surface of the slide, close to one side of 

 the hole in the stage, which would con- 

 dense the light and reflect it very oblique- 

 Iv with the mirror central. 



F. H. GowEN. 



\Vf:st Newhurv, Mass. 

 April 28th, 1884. 



[The diagram shows a ray of light pass- 

 ing from the left-hand edge of the mirror 

 to the right-hand edge of the slide — the 

 latter being represented in section at right 

 angles to its length — and from thence re- 

 flected upon the object. — Ed.] 



o 



Clearing Fluid, 



To THE Editor : — I find in practice 

 that about equal parts of Squibbs' abso- 

 lute alcohol and eucalyptus oil forms a 

 very good clearing fluid for animal or 

 vegetable tissues. When the tissues are 

 freshly cut I place them in commercial 

 alcohol for a few minutes. I next trans- 

 fer them to the clearing fluid, as above 

 described, for a period of about ten min- 

 utes. They are next placed in pure euca- 

 lyptus oil, which removes the alcohol ; a 

 few minutes' immersion will suffice. When 

 they are ready to be mounted in balsam I 

 sometimes add a few drops of pure car- 

 bohc acid to the clearing fluid, but the 

 latter may be dispensed with. I have 

 made a number of very clear mounts in 

 this way. 



It is not well to keep tissues longer than 

 necessary in the fluid. Vegetable tissues 

 become hardened and brittle when kept 

 several days in the clearing fluid. 



Thomas Taylor, M. D. 



o 



Questions about Mounting. 



To the Editor : — Several of the fine 

 diatom slides I have, by Moller, are hav- 

 ing the covers cracked ; I suppose it is 

 caused by shrinking of balsam. Would 

 it be a good idea to run a Bell's cement 

 ring around them ; they are not cemented 

 at all ? My experience of white zinc ce- 

 ment agrees with yours. 



In speaking of Box R in the March 

 number, of No. 2 you say 'this one has a 

 bubble in it, but that may have been pur- 



posely left.' Where does the purpose 

 come in ? I never had the slightest diffi- 

 culty in enclosing bubbles, and shall here- 

 after consider all bubbles in my mounts 

 left on purpose. 



[The above is a portion of a letter not 

 sent for publication, but it affords an op- 

 portunity to answer some questions that 

 are not unlikely to arise from time to time. 



The balsam slides had best be fixed by 

 rings of benzole or chloroform balsam or 

 damar. Bell's cement will do, but we 

 think a balsam or damar finish is neater. 



Bubbles are occasionally left in fluid 

 mounts, especially when the cells are 

 deep, under the impression that the air 

 they contain, being very elastic, prevents 

 injury to the cell from internal pressure 

 when the temperature rises. We confess 

 to grave doubts if such bubbles are of any 

 benefit whatever. — Ed.] 



The Congress Nose-piece. 



To THE Editor: — The enclosed affi- 

 davit is a sufficient answer to Prof. Mc- 

 Calla's letter, and as he has made so many 

 erroneous statements I beg leave to doubt 

 anything further from him ; and more es- 

 pecially after seeing a copy of his so-called 

 drawings in the April number of your 

 journal, which 1 believe to have been ex- 

 ecuted since he received a sample of my 

 nose-piece. In proof of my assertion I 

 would say that when Prof. McCalla first 

 spoke to me last August he then referred 

 to two pins or catches. I said then that 

 three were much better, as there was not 

 so much danger of sagging to one side 

 with three as with two. In further proof 

 that he referred to two pins I will quote 

 these few words from a letter written to 

 me by Mr. E. Pennock : ' Remember that 

 in a general way that it was a sort of bay- 

 onet-catch arrangement, and he [Prof. 

 McCalla] thought that it would require 

 careful workmanship to make it grasp 

 both sides at once.' When Dr. Mohr was 

 in my shop I showed him drawings that 

 I have in my note-book, and which are 

 dated September ist, 1883. If Dr. Mohr 

 is the person referred to as having been 

 shown the drawings I am sure he would 

 not willingly assert that I even so much 

 as intimated that they were made by 

 Prof. McCalla. I would have you know 

 that the drawings 1 have in my note-book 

 are those that I made myself; but what 

 the Professor means by stating in one sen- 

 tence that he made them and in the fol- 

 lowing sentence saying that he does not 



