1400 



Journal of Applied Microscopy 



this means the depth of focus necessary in any case can be obtained. The 

 lowest objective that will resolve the details wanted is selected, and then the 

 requisite power is obtained by camera extension ; this preserves at all times the 

 relative depth of focus. It is true that a histological section can be so thick or 

 prepared so poorly that the photography of it is difficult. A better section 

 should be made (and this is one reason for the use of photomicrography — it will 

 at once lead to the preparation of better microscopic slides). Any section can, 

 however, be so photographed as to show all that can be seen at any one look, 

 and by repeated exposures all can be shown. Fig. 2 was made with an 8 mm. 

 objective and a No. 4 projection eye-piece, and a camera extension of four feet, 



Fig. 2. — Frog's blood ; hJEmatoxylin-eosin stain, x 400. 



and shows the same things in flatness of held and depth of focus for its power, 

 400 diameters, that Fig. 1 does for its. 



Fig. 3 is a section of onion root with chromosomes lying in several different 

 planes, and shows the same for 1500 diameters. It was made with a 2 mm. oil 

 immersion, apochromatic objective, and a No. 4 projection eye-piece, with a 

 camera extension of thirty-seven inches. Fig. 4, Fig. 5, and Fig. G, were made 

 with the same combination. 



Fig. 6 is a blastula of ascaris ; it was photographed from an unsectioned 

 blastula ; the instrument was focused on the midsection of the ball of cells ; the 

 light had to pass through the lower cells before, and the upper cells after passing 

 the points shown ; this is a means of sectioning with the microscope. Fig. 1 

 represents low-power work. Fig. 2 medium-power work, and the remaining figures 



