1881.] 



MICEOSCOPICAL JOUKNAL. 



87 



obtained from any stationer, is a cheap 

 and satisfactory staining fluid. One 

 or two minutes immersion in this is 

 usually sufficient time to give the 

 bacteria a deep violet color. Those 

 who have not resorted to this method 

 will be astonished at the facility with 

 which it is practiced and with the 

 variety of forms which may be de- 

 monstrated at a moment's notice, 

 without a resort to culture-experi- 

 ments or to a search in ditches and 

 sewers. The mouth, the rectum, the 

 extremity of the urethra in the male, 

 and the vagina in the female, are 

 constantly supplied with an incredi- 

 ble number of these minute, vegetable 

 organisms, and a great variety of 

 forms may be observed, especially in 

 the discharges from the bowels. The 

 slightest possible smear of saliva 

 scraped from the surface of the 

 tongue, of vaginal mucus, or of fecal 

 matter dried upon a slide, stained 

 with violet ink and washed with a 

 gentle stream of water, will furnish 

 ample material for study and will 

 serve as a practical demonstration of 

 the extensive distribution of the bac- 

 teria. To obtain a satisfactory view 

 a good ^-inch objective will be re- 

 quired, and for the smaller species a 

 lens comparable to the ^^-inch of 

 Zeiss is desirable. 



Bacteria may often escape observa- 

 tion, not only because of their minute 

 size, but because they may have very 

 nearly the same refractive index as 

 the fluid which contains them. Asser- 

 tions, therefore, as to their tiot being 

 found in certain secretions, etc., will 

 have but little value unless it is 

 shown that this or some other effi- 

 cient method of staining has been 

 resorted to, and the objective em- 

 ployed is mentioned. 



Geo. M. Sternberg, 

 Surge 071, U. S. Army. 



Baltimore, Md. 



[Dr. Sternberg has sent us a num- 

 ber of photograph-prints of different 

 objects prepared according to the 

 method described above. Although 



he states that they do not show his 

 best results, they certainly give evi- 

 dence of the real excellence of the 

 process. Among them is one of Bac- 

 terium iermo, which is usually re- 

 garded as an exceedingly difficult 

 object to photograph. The organism 

 is well portrayed, magnified 1,500 dia- 

 meters. Some swarm-spores of an 

 alga are remarkably well-shown, as 

 are also some other cells which are 

 designated as Protococcus. — Ed.] 



The Physics of Yision with the 

 Compound Microscope. 



{Continued?) 



According to Professor Abbe's theo- 

 ry, the objective and ocular must be 

 regarded as two pieces of apparatus, 

 perfectly distinct from each other, 

 both as to their construction and 

 functions. For a thorough under- 

 standing of this subject, it will be 

 necessary for the microscopist to dis- 

 possess his mind of the common idea 

 that the objective and ocular are so 

 intimately combined in the compound 

 microscope, that the faults of one can 

 be corrected by alterations of the 

 other. One fact which lies as the 

 very foundation of this theory, is 

 that the objective forms the image 

 and the ocular merely spreads that 

 image over a greater area, magnify- 

 ing the faults without correcting 

 them. With our present knowledge 

 and materials, it is not possible to 

 construct either a perfect objective 

 or ocular. There are certain faults 

 inherent to the methods now em- 

 ployed for correcting aberrations, 

 although some recent experiments of 

 Professor Abbe, in which he made 

 use of lenses filled with fluids having 

 various refractive and dispersive 

 powers, have shown that very perfect 

 correction would be possible, by well- 

 known methods, if we could obtain 

 the proper materials. The limited 

 time only permits me to allude to a 

 few of the imperfections. Both chro- 

 matic and spherical aberrations are 



