92 THE AMERICAN MONTHLY [April, 



of the pages, by which means the record of each slide is uninterrupted, 

 and opportunity is given for the substitution of other data according to 

 the habit or preference of eacli student. By entering promptly every 

 slide prepared or otherwise obtained, and recording such data as may 

 then be known concerning it, or as may happen to be acquired after- 

 ward, much useful information will be saved, and the value of any col- 

 lection, whether large or small, will be greatly increased. 



Copies can be obtained, carriage paid, from the author, at the cost 

 of $4.00 for 1,000 slides, $6.00 for 3,000, $S.oo for 3,000. $10.00 for 

 4,000 in two volumes, and for larger sets $3.00 for each 3,000 of addi- 

 tional capacity. 



Focussing the Chemical Rays. — Q. Is not the chemical focus, on 

 account of the greater refrangibility of the chemical rays, nearer the 

 objective than the visual focus, and should not the objective be moved 

 nearer to the object in order to throw the chemical focus back to the 

 screen } This may not be very important, as a lens perfectly corrected 

 for chromatic aberration would probably render the chemical and vis- 

 ual focus nearly or quite coincident. — J. M.Edwards. A. The cor- 

 respondent is quite right in his suggestion that the focus of the chemical 

 rays is nearer the front of the objective than the focus for the more lu- 

 minous rays, on account of their greater refrangibility. Nevertheless, 

 my own statement is correct, that the objective must be withdrawn 

 from the object to focus the chemical rays on the screen. For with the 

 ordinary over-corrected objectives the focal plane for the actinic rays is 

 further away than that for the other rays. — R. Hitchcock. 



MICROSCOPICAL SOCIETIES. 



Washington, D. C, — L. M. Mooers, Sedy. 



103d Aleetlng, JSIarch 25. — A paper was read by Dr. V. A. Moore, 

 on micro-organisms in urine, with special reference to those forms 

 which cause its ammoniacal fermentations. He exhibited plate and 

 tube cultures showing the characteristics of growth and development 

 of these bacteria and their action on culture media. Dr. C. H. Stow- 

 ell, late of Ann Arbor, Mich., and founder of The Microscope^ was 

 elected to membership. 



104th Meetings April 8. —The Life History of Micro-organisms, 

 with its Relation to the Theory of Evolution, was the subject of a 

 paper by Dr. Robert Reyburn. The paper was full of interest, and 

 the discussion which followed was participated in by Dr. C. H. Stow- 

 ell, Dr. Thomas Taylor, Dr. V. A. Moore, and Dr. Reyburn. 



o 



San Francisco, Cal., — Wm. E. Loy, Sec'y. 



March 26, i8go. — The secretary reported the usual additions to the 

 libraiy of periodicals and proceedings, including The Quarterly 

 Journal of Microscopical Science iox February. R. H. Freund and 

 John D. Coulie were elected active members and the application of Dr. 

 E. S. Clark was received. 



The paper of the evening was by Carl H. Eigenmann, Ph. D., on 

 " The Genesis of Chromatophores in Fishes." Mr. Eigenmann has 



