CHAPTER V 

 METHODS OF OBSERVING MICRO-ORGANISMS 



IT is of the utmost importance to examine micro-organisms 

 alive, and as nearly as possible in their normal environment, then to 

 supplement this examination by the study of dead and stained 

 specimens. 



The study of the living organism has the advantage of showing 

 its true shape, size, grouping, motility, reproduction, and natural 

 history. It has the disadvantage of being somewhat difficult because 

 of its small size and transparency. 



So long as bacteria were observed only in the natural condition, 

 however, it was impossible to find them in the tissues of diseased 

 animals, and it was not until Weigert suggested the use of the anilin 

 dyes for coloring them that their demonstration was made easy 

 and their relationship to pathologic conditions established. 



The beauty and clearness of stained specimens, and the ease 

 with which they can be observed, have led to some serious errors 

 on the part of students, who often fail to realize the unnatural con- 

 dition of the stained bacteria they observe. It only needs a moment's 

 consideration to show how disturbed must be the structure of 

 an organism after it has been dried, fixed, boiled, or steamed, 

 passed through several chemic reagents, dehydrated and impreg- 

 nated with stains, etc., to suggest how totally unnatural its appear- 

 ance may become. 



It is, therefore, necessary to examine every organism, under 

 study, in the living condition, and to control all the appearances 

 of the stained specimen by comparison. 



I. THE STUDY OF LIVING BACTERIA 



The simplest method of observing live bacteria is to take a 

 drop of liquid containing them, place it upon a slide, put on a 

 cover, and examine. 



While this method is simple, it cannot be recommended, as 

 evaporation at the edges causes currents of liquid to flow to and 

 fro beneath the cover, carrying the bacteria with them and making 

 it almost impossible to determine whether the organisms under ex- 

 amination are motile or not. Should it be desirable that such a 

 specimen be kept for a time, so much evaporation takes place that 

 in the course of an hour or two it has changed too much to be of 

 further use. 



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