CHAPTER V. 



SPECIAL PART. 



I. NON-PATHOGENIC BACTERIA. 



Micrococcus Prodigiosus, Bacillus Indicus, Sarcinse, Bacillus Megaterium, 

 Potato Bacillus, Bacillus Subtilis, Root Bacillus ; Micro-organisms in 

 Milk, Bacillus Cyanogenus, Bacillus Violaceus, Bacillus Fluorescens, 

 Phosphorescent Bacteria, Bacterium Termo, Bacillus Spinosus, Spirilla, 

 Spirillum Rubruni, Spirillum Concentricum. 



I. HAVING now made some acquaintance with the general char- 

 acteristics of the bacteria as a class, let us pass over to the treat- 

 ment of their particular species. 



First of all, we will briefly consider some non-pathogenic micro- 

 organisms; for though they possess less interest for us, there are 

 some among them which deserve our attention, both on account of 

 their wide distribution or frequent occurrence and on account of 

 their special peculiarities. 



If within this restricted circle we further confine ourselves to 

 those bacteria which have been sufficiently studied and have be- 

 come sufficiently well known to c eserve special mention, our selec- 

 tion from among the great number of non-pathogenic micro-organ- 

 isms which have been described of late will not be particularly 

 extensive. 



The mode of our investigations will always remain according 

 to modern methods. In the first place, the hanging drop shows us 

 the form and appearance of the micro-organism under examina- 

 tion; the same examination also shows us whether spontaneous 

 movement is perceptible or not, and gives us information on the 

 question of spore-formation. The cover-glass preparation perfects 

 the first part of the examination, and settles the question of be- 

 havior under the influence of staining matters. The breeding be- 

 gins from the glass plate; the peculiarities of the colony, which is 

 the starting-point of the pure culture, already betray to us some of 

 the relations of the bacterium under examination to the solid food 

 media, specially to gelatin. Next comes the test-tube culture on 

 different media gelatin, agar-agar, and blood-serum; lastly, the 



