118 



THE AMERICAN MONTHLY 



[June, 



deposits, crystals, pathological specimens, 

 mineral sections, diatoms, etc., etc., for 

 mounting, and will show how to mount 

 dry and in different media. Several in 

 the same line of work may show their in- 

 dividual methods at the, same time.' 



This seems to be one of the best schemes 

 yet devised for popularizing the use of the 

 inicroscope, and we trust the members of 

 the society will support the effort well. 



— We are authorized to state that the 

 Rev. W. H. Dallinger, of England, is ex- 

 pected to be present at the meeting of the 

 American Society of Microscopists, at 

 Rochester. 



— It is stated that Bellevue Hospital 

 Medical College is to have a laboratory 

 especially designed for microscopical in- 

 vestigations, through the liberality of Mr. 

 Andrew Carnegie, of Pittsburg, who has 

 given the college the sum of $50,000 to be 

 expended in the erection of a new build- 

 ing and the purchase of apparatus. 



CORRESPONDENCE. 



Mounting. Catching Insects. 



To THE Editor :■ — Your articles and 

 hints about mounting in the Journal are 

 invaluable to me, though I do not get 

 time to use them all, as I can only work 

 about one evening a week. Have mount- 

 ed some good slides of forammifera from 

 sand shaken from Mediterranean sponges 

 at a drug store. Was very successful 

 in killing hydra last night by the hot- 

 water method, but did not get far enough 

 to mount any. I shall try it in a few days. 

 A mounting needle bent like a hook at 

 the end, dipped in alcohol, is the best way 

 I have found for capturing small insects 

 on windows, under stones and boards. 

 Have used it for years, and the insect 

 always is drawn into the drop included in 

 the hook. Dipping the needle into the 

 alcohol frees the insect from the drop and 

 loads the needle again, and the capturing 

 goes on easily, surely, and rapidly. Even 

 the evanescent spring-tails can be taken 

 in this way. 



[The above method of catching insects, 

 first desci'ibed on page 59, deserves to be 

 remembered. We would suggest that, 

 owing to the hardening and stiffening 

 effect of alcohol, it might be better to dip 

 the needle into concentrated carbolic acid 

 to free the insects. In carbolic acid they 

 do not draw up their limbs as in alcohol, 



and after a few moments in the acid they 

 are ready to be mounted in balsam or in 

 any other medium. — Ed.] 



o 



Resolution of Amphipleura. 



To THE Editor : — Having experi- 

 mented occasionally during the last two 

 months on A. pellucida, I find that this 

 diatom is well resolved without the use of 

 a mirror or other illuminating apparatus, 

 by direct sunlight above the stage. The 

 microscope should be so placed that the 

 light may fall on the circumference of the 

 stratum of immersion fluid, obliquely to 

 the upper surface of the slide, and care 

 should be taken to have one end of the 

 frustule point towards the sun. As the 

 discovery of this method of illumination 

 was merely accidental, it has occurred to 

 me that it may have some bearing on the 

 resolution of A. peUiicida by central light. 

 Take for example the experiment of Prof. 

 Forbes (this Journal, June, 1883, page 

 118) where it is noted that ' while the res- 

 olution is perfect when the diatom lies 

 transverse to the stage, they disappear as 

 the direction is changed.' As the Profes- 

 sor suggests, this would not have occurred 

 if the resolution had been effected by cen- 

 tral light. It seems highly probable that 

 in Prof. Forbes's case, as in mine, the mi- 

 croscopes were accidentally placed in 

 such a position that the direct sunlight 

 above the stage resolved the diatoms. 



My objective is a -^-^ of 110° B. A., by 

 H. R. Spencer & Co. It resolves Dr. 

 Sloan's A. pelhicidaixihdXi'AxvL (this Jour- 

 nal, Oct., 1883, page 198) by lamp-light 

 and concave inirror, both above and be- 

 low the stage, and by direct sunlight above 

 the stage. The resolution is better with 

 the light above than below the stage. 

 Possibly the immersion fluid acts in some 

 way as a condenser. 



F. H. GowEN. 



West Newbury, Mass. 

 March 20th, 1884. 



Resolution by Central Light. 



To the Editor: — I recently sent you 

 a note in which I stated that A. pellucida 

 is easily resolved by direct light above the 

 stage, and suggested that this might be a 

 possible explanation of the resolution of 

 this diatom by ' central light.' I have 

 since succeeded in resolving A. pellucida 

 in balsam by sunlight, with the mirror in 

 a strictly central position ; but on investi- 

 gating the course of the illuminating rays 

 I found that the resolution was effected by 

 light reflected within the slide, from one 



