IV INTRODUCTION. 



tically, on a fixed vertical support. When it is required to 

 manipulate with forceps and scissors under still higher magni- 

 fying powers, the little preparation cell should be fastened upon 

 a blackened wooden block, several centimeters in height, and 

 resting on the table. The arms being thus in a nearly hori- 

 zontal position, and well supported, permit the observer to 

 work with greater steadiness. In making preparations with 

 strong lenses, the nose of the observer necessarily comes into 

 close proximity with the object, and the bridge of the nose can 

 be used as a point of support for the cutting instrument em- 

 ployed. When sections are made with scissors and forceps 

 under strong lenses, it is usually necessary that the object 

 should be firmly fixed, and, at the same time, very steady 

 movement on the part of the cutting instrument is required. 

 It is in particular quite indispensable that some kind of sup- 

 port should be given, if it be required, to make clean and thin 

 sections of small and delicate objects. 



If the left eye be applied to the lens, the right hand can 

 with great certainty direct a fine pair of scissors balanced on 

 the bridge of the nose whilst the left hand fixes the object. 

 For the fixation of very delicate objects, substantial forceps, 

 with very sharp, smooth points, will be found serviceable. If 

 it be desired to work by means of direct light with a com- 

 pound microscope, weak objectives, such as the No. 5 of Hart- 

 nack's microscope, or those corresponding to them of other 

 instruments, can alone be employed. Formerly weak com- 

 pound microscopes, which gave erect images, were used for 

 the preparation of objects. These so-called dissection micro- 

 scopes are not, however, really necessary, since the opposite 

 movement of the hand demanded for the inverted image is 

 soon acquired by practice. 



The examination of objects can, in like manner, be under- 

 taken with transmitted light, both with the aid of simple 

 and of compound microscopes. In regard to the use of the 

 former, there is little to be added to what has already been 

 said. For the examination of objects with transmitted light, 

 it is obvious that the support must be transparent, and the 

 objects must themselves be illuminated by the reflected light 

 proceeding from either a mirror or a prism. Simple micro- 



