1730 Journal of Applied Microscopy 



an upright camera of any description. A base board on which the microscope 

 rests, to which are attached two upright posts carrying a camera capable of 

 being extended thirty inches above the object, is all that is necessary. The 

 light used is daylight from a clear sky exactly as one uses it in microscopy, no 

 color screens or cooling cells or field diaphragms ; the only substage arrange- 

 ments are an adjustable Abbe and iris diaphragm. The lenses and eyepieces 

 must of course be the best obtainable for this purpose. By this arrangement the 

 light is not sufficient to enable one to focus on the ground glass. These ladies con- 

 cluded that there must be some relationshipbetween the focus for ordinary micros- 

 copy and that for photomicroscopy at any given extension ; by experiment they 

 found that any one can select a spectacle-glass with which if he focuses his instru- 

 ment, the focus will also be right on the sensitive plate at a particular extension. 

 These glasses can be bought of any optician; they are labeled D'g- D/i) DK') 

 etc., up, and D-^, D-i^, etc., down. With a Zeiss '2 mm. apochromatic 

 objective, a IGO mm. tube-length, a No. 4 projection eyepiece, a camera exten- 

 sion of 29^ inches, and an operator slightly on the sunny side of thirty, a D 2 

 lens will approximately correct the focus ; younger operator, higher number ; 

 older, lower. A good photographer can focus his second exposure correctly as 

 follows : get an approximate focus on a middle detail in a thick section having 

 sharp details in several planes ; make an exposure and develop the negative ; 

 with the negative or a print in hand select an eyeglass that gives the same image 

 as the one seen in the negative; this will be just the glass to use for focusing 

 under the given conditions. In the same way a glass can be chosen for any 

 other assemblage of lenses and conditions. This is the only sort of cheap outfit 

 I have yet seen that I did not regard as too expensive. These ladies have ren- 

 dered a valuable service to all who desire to practice photomicrography with an 

 inexpensive outfit. 



Figs. I, 2, 3 and 4 all represent stages in the first kariokinetic division of the fertilized egg 

 of Ascaris. All are made with a 2 mm. objective and No. 4 projection eyepiece, with a camera 

 extension of 37 inches. All show a sharp focus in the respect in which it was intended to be 

 sharp. 



Earlham College. D. W. Dennis. 



ELEMENTARY MEDICAL MICRO-TECHNIQUE. 



For Physicians and Others Interested in the Microscope. 



CoPVKK.H I KD. 



IV— TETANUS. 



The bacillus of tetanus is found in the pus at the point of inoculation. 

 Spread a thin film of the pus on a clean cover-glass held in a Cornet forceps, 

 using a platinum loop, which should be sterilized before and after using. Pass 

 the cover-glass, film side up, three times through the flame of an alcohol lamp 

 or Bunsen burner. Stain with carbol fuchsin, methylen-blue or methyl-violet, 

 putting on the film side of the cover a liberal quantity of the stain selected. 

 Stain from one to five minutes, wash in water, and dry between filter paper and 



