42 METHODS OF STUDYING MICROORGANISMS 



of bacteria cannot be demonstrated by stain or cultural 

 methods, it may sometimes be shown by injecting the 

 suspected material into animals. If the animal fall 

 sick or die one can then obtain the germs for study. 

 It is most useful in discovering the presence of the 

 tubercle bacillus, an organism not easy to find by 

 direct examination. 



Protozoa. The study of protozoa varies according 

 to the source. The parasite of malaria may be found 

 by direct microscopic examination of the fresh blood. 

 This is also true of the organism of sleeping sickness. 

 The protozoa causing dysentery require the mainte- 

 nance of a definite temperature for a long time, and 

 this is achieved by the use of a hollow slide filled with 

 warm water. These organisms are cultivated arti- 

 ficially only with great difficulty, and the use of special 

 stains is required for the purpose of practical clinical 

 diagnosis. 



STERILIZATION 



For a better understanding of the technique of 

 laboratory procedure, the preparation of the food- 

 stuffs or media on which bacteria thrive will be briefly 

 considered. They are prepared according to carefully 

 worked-out formulae, which are the result of long 

 experimentation. They are stored or distributed in 

 glassware, which is of the non-corrosive type. This 

 glassware is cleaned with soap and water, sand or 

 alcohol, and rinsed with distilled water. It is then 

 sterilized by hot air. The glassware and media are 

 sterilized because bacteria are ubiquitous and appa- 

 ratus and foodstuffs wholly free from microorganisms 



