84 MICROSCOPY 



standard parts, like mass-produced machinery, whereas others contain 

 very special individual components. One of the tasks of those biologists 

 who were able for the first time to examine cells in detail was to describe 

 what they saw. Descriptions require words, mostly nouns and adjectives. 

 Because of the great diversity of living things, a tremendous vocabulary 

 of strictly biological terms arose. Any beginning biologist at that time 

 faced the initial barrier of learning this vocabulary. To a certain extent 

 this is still true, but unfortunately, there are some who feel that this 

 vocabulary is biology and consider the terminology more important than 

 the concepts the words were invented to describe. 



At any rate, the importance of the microscope in the development of 

 the science of biology cannot be minimized. The convenient models 

 available now are used almost daily in every laboratory. The materials 

 used by the experimental biologist are made up of cells which are too 

 small to be seen by the unaided eye. The investigator interested in 

 muscle contraction must consider changes in the appearance of muscle 

 cells. Microorganisms are favorable experimental organisms, but must 

 be examined routinely. Because living cells are below the limit of visi- 

 bility, the compound microscope will always be one of the most useful 

 tools to either the descriptive or the experimental biologist. 



The compound microscope 



The compound microscope is so called because it contains two sets of 

 lenses: an objective lens, which produces an image, and an eyepiece or 

 ocular, which further magnifies the image. The magnification available 

 is the product of the magnifications produced by the separate lens units. 

 The objective and ocular systems of the compound microscope are elabo- 

 rate combinations of individual components fitted together according to 

 a formula which is intended to provide the best possible view of the 

 object being examined. 



Microscopes differ in details of construction, partly because of competi- 

 tion among producers, but all are constructed according to a general 

 pattern. Figure 8-1 shows a typical microscope, from which the major 

 parts can be identified. The two lens systems, the objective (A) and the 

 ocular (B), are at opposite ends of a body tube (C). The object to be 

 examined is placed on a glass slide on the stage (D) just below the 

 objective lens. The object is illuminated from below through a hole in 

 the stage, and the light may be focused by a substage condenser (E) 

 and regulated by a diaphragm or other devices. The microscope is 



