INTRODUCTION. 



Micrococci, for instance, which are, in reality, extremely 

 different, may look very much alike. The differences are 

 usually apparent when the bacteria are grown artificially. 

 The cultivation is done for the most part in FIG. 2. 

 test-tubes containing some material which fur- s^"y 

 nishes suitable food. The nutrient materials c 



'':' '-;,. .,. rf*. 



most used are meat-extract and peptone, which, 

 dissolved with salt in water, constitute nutrient 

 bouillon. Ordinary gelatin, or a vegetable gel- 

 atin called agar-agar , may be added to the 

 bouillon when a solid culture-medium is de- 

 sired. Before these substances can be used for 

 the cultivation of bacteria all other bacteria 

 which they might contain must be destroyed by 

 heat. 



When bacteria are to be conveyed from one 

 tube to another, or from a tube to a glass slide, 

 in order to examine them with the microscope, 

 the manipulation is performed on a platinum 

 wire fastened into a glass rod. The rules laid 

 down for the management of the tubes and the 

 platinum wire (Part I., Chapter VIII.) must ~ . 



Test-tube con- 

 be carefully followed. There is little or no dan- taining cui- 



ger in bacteriological work if the proper pre- 

 cautions are conscientiously observed; but carelessness may 

 lead to disastrous and even fatal results, as has happened 

 more than once. 



Finally, the effects of bacteria in bringing about disease 

 may be tested on the lower animals. The proof that a par- 

 ticular species of bacteria causes a particular disease cannot 

 be considered complete unless the disease can be repro- 

 duced by introducing these bacteria into some animal. 



The student who wishes to pursue bacteriological study 

 in any direction farther than it is possible for the limits of 



