8o 



MORPHOLOGY AND CULTURE OF MICROORGANISMS 



FIG. 60. Types of spirilla. (After Williams.) 



GRADATIONS. The difference between these fundamental form 

 types is frequently very slight. It becomes a very difficult matter, 

 for instance, to distinguish at times between the micrococcus and the 

 bacillus. There is a number of bacteria, and among them the well- 

 known example of B. prodigiosus, which are described at one time by one 

 investigator as micrococci and at another time, or, by another inves- 

 tigator, as bacilli. The pneumonia germ is also another illustration 

 of an organism that occupies a dual position. Migula has suggested 

 a method of differentiating these which will be discussed under a 

 later head. The bacilli pass almost imperceptibly into the spirilla. 

 The cholera bacillus of Koch is in reality a spirillum. 



FIG. 6 1. Involution forms. Here are illustrated unusual forms of B. subtilis, 

 water bacteria, Bact. aceti, Bact. pasteurianum, bacteroids in root nodules, Bact. 

 tuberculosis, Bact. diphtheria. (After Fischer from Frost and McCampbell.) 



