CH. IX a] PROJECTION MICROSCOPE 249 



CHAPTER IX A 



THE PROJECTION MICROSCOPE 



One of the most useful and satisfactory means at the disposal of 

 the teacher of Microscopic Anatomy and Embryology for class demon- 

 strations is the Projection Microscope. With it he can show two 

 hundred students as well as one, the objects which come within the 

 range of the instrument. 



It is far more satisfactory than microscopic demonstrations, for 

 with the projection microscope the teacher can point out on the screen 

 exactly the structural features and organs which he wishes to demon- 

 strate, and he can thus be certain that the students know exactly what 

 is to be studied. Unless one employs a pointer ocular (Fig. 201). 

 there is no certainty that the student selects from the multitude of 

 things in the microscopic field the one which is meant by the teacher. 

 Like all other means, however, the projection microscope is limited. 

 With it one can show organs both adult and embryonic, and the gen- 

 eral morphology. For the accurate demonstration of cells and cell 

 structure the microscope itself must be used. As a general statement 

 concerning the use of the projection microscope for demonstration 

 purposes, it may be said that it is entirely satisfactory for objects and 

 details which show under the microscope with objectives up to 16 mm. 

 equivalent focus. For objects and details requiring objectives higher 

 than 1 6 mm. focus for ordinary microscopic observations, the projection 

 microscope is unsatisfactory for large classes. 



All specimens should be studied under the microscope by each 

 student personally ; however, it is much easier to recognize and 

 understand the complex structures and structural relations in an object 

 after they have been demonstrated by the instructor with the projec- 

 tion microscope. 



398. Projection Microscope. This is an arrangement of the 

 microscope such that an image of the object under the microscope is 

 thrown upon a screen of some kind. The picture on the screen is 

 looked at precisely as one looks at the pictures thrown on the screen 



