1883.] 



MICROSCOPICAL JOURNAL. 



239 



the different objects measured. Hence 

 the important question hinges, not 

 upon the absokite accuracy of the di- 

 visions of the micrometer, but upon 

 the quality of the objectives. 



Perhaps we of the present time are 

 inclined to over-estimate the advanta- 

 ges of our best objectives for the par- 

 ticular work now under consideration. 

 If we are endeavoring to establish ab- 

 solute sizes, it is important that the 

 sharpest definition of the disks should 

 be obtained ; but for relative sizes it 

 is not so essential, as anyone can un- 

 derstand. The point we desire to 

 make in this article is, that the work 

 of Gulliver and some others of his 

 time, possesses a value even to-day ; 

 for while their unit of measurement 

 may have been erroneous, and their 

 objectives inferior, the results are 

 probably as correct — that is to say, 

 as comparable among themselves — 

 as those that can be obtained now, 

 with the same magnifying powers. 



The author also refers to the differ- 

 ence in measurements made by two 

 observers under the same conditions. 

 It would be interesting to determine 

 just how much this difference is, for 

 blood-cells. It will probably be found 

 very insignificant between practiced 

 ' observers. The five per cent, is clearly 

 an extraordinary variation. It will be 

 remembered that Profs. Rogers and 

 Morley experimented to determine 

 the limits of accuracy in measure- 

 ments of ruled lines, working inde- 

 pendently, and their results were prac- 

 tically identical. But the variation 

 would undoubtedly be greater in the 

 case of blood-disks. 



The whole article points to the ne- 

 cessity of adopting a standard micro- 

 meter, which we have repeatedly 

 urged upon microscopists, and we 

 trust it will not be long before the 

 standard is fixed, and deposited where 

 it can be used for purposes of com- 

 parison. 



Our readers will, we doubt not, look 

 forward with much interest to the 

 article promised by Mr. Vorce, for a 

 future number of the Journal. 



NOTES. 



— It is often necessary to employ mac- 

 erating fluids in the study of microscopic 

 structures, and in the study of coelenterata 

 the following solution for the purpose has 

 been used by O. and R. Hertweg, with 

 good success. It consists of acetic acid 

 I part, osmic acid ^ part, sea-water 1,000 

 parts. By maceration in this fluid, nerve- 

 cells, mussel-cells, etc., can be isolated 

 and their forms thus observed. 



— Dr. Geo. M. Sternberg recently 

 spoke on the subject of micrococci be- 

 fore the Biological Society, of Wash- 

 ington. In attempting to give an idea of 

 the minuteness of some of the micrococci, 

 he stated that a drop smaller than a pin- 

 head might contain five hundred millions 

 of them. 



CORRESPONDENCE. 



The Tongue of the Blow Fly. 



To THE Editor. — In following out the 

 directions given in the admirable article 

 entitled "'Unpressed Mounting for the 

 Microscope," reprinted at page 229, Vol. 

 3 of this Journal, I met with one diffi- 

 culty which may also have been encoun- 

 tered by others. I found that while it is 

 an easy matter to catch and decapitate 

 your blow fly, unfortunately he will not 

 always protrude his tongue properly dur- 

 ing the operation, and my experience is 

 that the tongue remains forever after 

 fixed in the position that it happens to be 

 when life in the fly becomes extinct. To 

 remedy this I tried the plan of immersing 

 the living insect in alcohol, and with per- 

 fectly satisfactory results. At the mo 

 ment of death the tongue is forcibly pro- 

 truded to its entire length. Even the 

 short proboscis of the house fly is satis- 

 factorily displayed. 



I tried carbolic acid in the same way, 

 but the results were not nearly as good, 

 and besides alcohol is a much nicer fluid 

 to handle. 



A. L. Woodward. 



A Correction. 



To the Editor. — Will you allow me 

 to ask the attention of the readers of the 

 November Journal to the incorrect ar- 



