CHAPTER V. 



METHODS OF OBSERVING BACTERIA. 



IT is of the utmost importance to examine bacteria alive 

 and as nearly in their normal environment as possible, 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, reproduc- 

 tion, and natural history. It has the disadvantage of being 

 somewhat difficult because of its small size and trans- 

 parency. 



vSo 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 condition of the stained bacteria they observe. 

 It only needs a moment's consideration to show how dis- 

 turbed must be the structure of an organism after it has 

 been dried, fixed, boiled, or steamed, passed through several 

 chemic reagents, dehydrated and impregnated with stains, 

 etc., to suggest how totally unnatural its appearance may 

 become. 



It is therefore necessary to examine every bacterium, 

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

 the appearances of the stained specimen by comparison. 



L 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. 



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