PAKT SECOND 

 STRUCTURAL ELEMENTS 



PRELIMINARY STUDY 

 FORM OF OBJECTS 



From a single and hasty view of bodies under the microscope, 

 we are liable to form erroneous ideas of form. Either a sphere, 

 disc, ellipsoid, ovoid, or cone may be so viewed as to present a 

 circular outline. It therefore becomes important to view objects in 

 more than a single position. This can easily be accomplished with 

 isolated particles by suspension in a liquid. In this way the true 

 shape of a blood -corpuscle, e.g., may be determined. 



Again, much information concerning the actual form of bodies 

 may be gained by a proper adjustment of the fine focusing screw. 

 You maj' remember that the depth of the field of view in the micro- 

 scope is exceedingly slight. Speaking accurately, only a single 

 plane can be seen with a single focal adjustment ; but by gradually 

 raising or lowering the t tube of the microscope the different parts 

 of a body may be focused and studied, and an accurate idea of 

 form secured. 



With a glass rod place a drop of milk, which has been pre- 

 viously diluted with three parts of water, on a slide, and put a cover- 

 glass thereon, as in Fig. 23. Focus first with the low-power (L). 

 A multitude of minute dots are observed. Then change to the high- 

 power (H), and the dots will resolve into circular figures. Select 

 one of the smaller particles, and, as you raise the focus, the center 

 of the figure retains its brilliancy, while the edges become dark or 

 blurred, showing convexity. Reverse the focus, and the center 

 again retains its sharpness long after the edge has become blurred. 

 The figure, then, is a spheroid. These bodies are fat -globules. 

 Particles of free fat always assume the spheroidal form when sus- 

 pended in a liquid. 



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