1160 



Journal of Applied Microscopy 



inary to this, however, the substage condenser has been racked up with the 

 coarse adjustment until it brings the image of the crater into focus at the level 

 of the object. If the camera has not been adjusted with reference to the optical 

 bench, it is now arranged so that the image of the crater falls in the center of 

 the ground glass. Provided the substage condenser is properly centered, the 

 linear adjustment of the combination is complete. 



The next step is to arrange the object with reference to the condenser and 

 the objective which is to be used in making the negative. I have found it 

 advantageous to connect these three elements with homogeneous immersion 

 fluid and for a condenser employ the " parachromatic " oil immersion form made 

 by Watson & Sons. The objective is an apochromatic 'I mm. of Zeiss. 



Figure 2. — Transformation stages between tlie telophase of the spermatogonia and the ]irophase of the first 



spermatocytes. The gradual accimuilation of the chromatin into a thread may he noted. 



Successive stages shown at " a ", " b ", and " c ". Same object. 1000 diameters. 



For a number of reasons, it is convenient to interpose temporarily an 

 incandescent gas lamp in the substage series while getting the proper focus and 

 adjustment of the object with the eye. When this adjustment has been accom- 

 plished, it remains only to get the final projection of the image upon the ground 

 glass of the camera before the exposure is made. 



The projection eyepiece is now substituted for the observation ocular, which 

 has been used up to this time, and an image thrown upon the small screen which 

 still hangs upon the front of the camera. Here an approximate focus of both 

 object and source of illumination is obtained and the composition of the picture 

 studied. If this is satisfactory, the screen is removed, the camera pulled forward 

 and joined to the microscope, and connections made between the fine adjust- 

 ments of the tube and of the substage condenser with rods that lead back to the 



