92 The Microscope. 



what we are searching for as experts, in tracking the life and 

 behavior of various cells, and founding, or endeavoring to 

 found, a comparative morphology and physiology of cells and 

 unicellular bodies. 



V/AVS • 

 AND MEANS 



The Camera Obscura versus the Camera Lucida. — By 

 Henry G. Piffard, M. D. In drawing from the microscope three 

 methods are in vogue: 1. The observer studies the subject on 

 the slide, and when he thinks he has the outlines and details 

 sufficiently impressed on his mind, withdraws his eyes from the 

 tube and commits the mental picture to paper, using both eyes 

 in directing the movements of the pencil. 2. The observer, 

 looking down the tube with one eye (usually the left), is en- 

 abled to see the virtual image by a sort of autoprojection de- 

 lineated on a piece of white paper by the side of the microscope. 

 With the free right eye he guides the pencil in tracing on the 

 paper the magnified map of the object. 3. In using the camera 

 lucida a single eye is used for observing the object on the slide, 

 as well as for guiding the pencil in tracing its reflected image. 

 Method 1 requires a good memory and considerable skill as a 

 draughtsman. No. 2 less skill is required, but the knack of do- 

 ing it can only be obtained by practice. With No. 3, reason- 

 abl}^ normal vision is a prerequisite. The writer has for a long 

 time, perhaps always, been affected with astigmatism and 

 hypermetropia, to which advancing years have added pres- 

 byopia, and in consequence is unable to use the camera lucida 

 with satisfaction. In No. 1 binocular vision is employed in the 

 operation of drawing ; in No. 2 monocular vision, and in No. 3, 

 semi-ocular vision. 



The inconveniences referred to may be avoided by a simple 

 device which the writer has of late used with some satisfaction, 

 namely a right angled prism with silvered hypothenuse. This 

 should be mounted with a short tube extending from one of the 

 square surfaces and of suitable size to enter the tube of the 



