20 



THE AMERICAN MONTHLY. 



[January. 



looking over the illustrations in Stern- 

 berg's last edition of ' Bacteria.' The 

 photo-micrographs of groups of fungi have 

 an individuality that is lost in engravings. 

 The illustrations in this excellent little 

 work are certainly not all that might be 

 desired, but, as the doctor very aptly ob- 

 serves, it is ' easier to criticise than to 

 improve upon them.' 



It seems, when viewing a properly 

 illuminated object in the microscope — 

 every detail sharp and distinct — as though 

 the fixing of such a picture upon a sensi- 

 tive plate must be an easy matter. But, 

 only attempt to secure it — the delicate 

 gradation of color has disappeared. The 

 illumination is faulty, and probably weak 

 in actinic rays — there is only the single 

 plane in focus, as you can no longer coax 

 up detail after detail with the micrometer- 

 screw of the fine adjustment — and, if the 

 student has only the usual amount of 

 patience, he is apt to give up in disgust 

 before he has hardly begun. 



After all this circumlocution 1 want to 

 say this : Photo-micrography is capable 

 of being made to secure results that will 

 give the author of their production the 

 very highest satisfaction as unimpeachable 

 scientific records. Such results cannot be 

 gotten without expensive appliances and 

 special surroundings. If it be the aim to 

 produce pretty little pictures of flies' 

 wings and the l.kc, why such may be 

 made with the expenditure of little money, 

 and with the production of only a mod- 

 icum of cholestearin. There is a poor 

 satisfaction in presenting a given result, 

 if you know some one else can do very 

 much better. Why not do it yourself bet- 

 ter, and so on, better, until you know it 

 represents the very best result attainable 

 with our present means ? 



I am very* glad, my dear Mr. Editor, 

 that you propose to give us a series of 

 papers on the subject of Photo-microgra- 

 phy, for, certainly, no one can be better 

 prepared than you to survey the ground 

 that has been trodden, and to indicate 

 means for successful work. 



Maurice N. Miller, M. D. 

 o 



'Rotifer Nests.' 



To THE Editor : — In volume iii of the 

 Journal, Mr. F. Wolle described a roti- 

 fer's nest or gall on VaiicJieria geniinata. 

 I have glanced over the indices of subse- 

 quent volumes without finding further 

 reference to the same interesting object. 

 The description is so clear that there is 

 little doubt, it seems to me, regarding its 

 identity with the gall of Notoviata IVer- 



neckii. A very satisfactory account of 

 this rotifer and its habits by Professor 

 Balbiani is given in volume ii, p. 530, 

 with plate xviii, of the Journal of the 

 Royal Microscopical Society. The para- 

 site has not been detected at Buffalc, 

 although sought after many times. 

 Buffalo, N. Y., D. S. K. 



Nov. 5, 1885. 



o 



Magnification. 



To THE Editor : — First. What is the 

 magnifying power of a one-inch lens at 

 10 inches between object and image ? 



Answer. 7.9 diameters. 



Second. What is the formula of a two- 

 inch eye-piece as used in the microscope, 

 not in the telescope ? 



Answer. A certain formula for a mi- 

 croscope eye-piece, as a standard, cannot 

 be given, owing to the variable conditions 

 to which the quality is s^ibjected. Be- 

 sides the tube-length, or rather the dis- 

 tance from the objective, the distance of 

 the eye from the eye-lens,- and also the 

 angular aperture (field) have a determin- 

 ing influence in the construction of the 

 eye-piece. 



Third. What is the magnifying power 

 of a two-inch eye-piece, 10 inches between 

 object and diaphragm ? 



Answer. The magnifying power of an 

 eye-piece is not varying with the distance 

 of the object. The magnifying power of a 

 two-inch eye-piece is just 6 diameters. 

 (See article, ' IVIagnifying Power,' page 11, 

 Catalogue, Gundlach Optical Company.) 



Fourth. Unable to answer. 



Fifth. What is the length of a ten-inch 

 tube ? 



Answer. Ten inches, 1 should think. 

 E. Gundlach. 



NOTICES OF BOOKS. 



Iritis: Its relation to the Rheumatic 

 Diathesis and its treatment. By Chas. 

 J. Lundy, A. M., M. D. (Pamphlet, 

 pp. 10.) 



The Anatomy and Physiology of Bacteria 

 and their relation to Health and Dis- 

 ease. By J. M. Selfridge, M. D. Oak- 

 land, Cal. (Pamphlet, pp. 29.) 



Exclianges. 



[Exchanges are inserted in this column without 

 charge. They will be strictly limited to mounted ob- 

 jects, and material for mounting.] 



Wanted : Cleaned St. Vincent material, for cash. 

 E. A. SCHULTZE, 

 Tompkinsville, Staten Island, N. Y. 



