VIII BACILLUS 85 



scale above the figure representing y^^ mm. magnified to the 

 same amount. The height of this book is a Httle over 18 cm. ; 

 this multiplied by 4,000 gives 7 2,000 cm. = 7 20 metres = 2362 

 feet. We therefore get the proportion — as 2362 feet, or 

 nearly six times the height of St. Paul's, is to the height of 

 the present volume, so the length of Fig. 14 is to that of 

 Bacterium termo. 



It was mentioned above that at a certain stage of putre- 

 faction a scum forms on the surface of the fluid. This film 

 consists of innumerable motionless Bacteria imbedded 

 in a transparent gelatinous substance formed of a proteid 

 material (Fig. 13, b). After continuing in the active con- 

 dition for a time the Bacteria rise to the surface, lose their 

 flagella, and throw out this gelatinous substance in which 

 they lie imbedded. The bacterial jelly thus formed is called 

 a zooglcea. Thus in Bacterium termo, as in so many of the 

 organisms we have studied, there is an alternation of an 

 active with a resting condition. 



During the earlier stages of putrefaction Bacterium termo 

 is usually the only organism found in the fluid, but later on 

 other microbes make their appearance. Of these the com- 

 monest are distinguished by the generic names Micrococcus, 

 Bacillus, Vibrio, and Spirillum. 



Micrococcus (P'ig. 15) is a minute form, the cells of which 

 are about 2/x (^^^ mm.) in diameter. It differs from 

 Bacterium in being globular instead of spindle-shaped and 

 in having no motile phase. Like Bacterium it assumes the 

 zooglaea condition (Fig. 15, 4). 



Bacillus is commonly found in putrescent infusions in 

 which the process of decay has gone on for some days : as 

 its numbers increase those of Bacterium termo diminish. 



