MORPHOLOGY AND CULTURE OF MICROORGANISMS. 



micrococci and at another time, or, by another investigator, as bacilli. 

 The pneumonia germ is also another illustration of an organism that 

 occupies a dual position. Migula has suggested a method of differentiat- 

 ing these which will be discussed under a later head. The bacilli pass 

 almost imperceptibly into the spirilla. The cholera organism has been 

 described as a bacillus as well as a spirillum. 



INVOLUTION FORMS. The form of bacteria is quite constant under 

 normal conditions, but very frequently they show abnormal or bizarre 



FIG. 19. Involution forms. Here are illustrated- unusual forms of B. subtilis, 

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

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



forms. These are known as involution forms (Fig. 19). It is some- 

 times suggested that these involution forms represent another stage in the 

 developmental history of the organism, and upon this supposition cer- 

 tain bacteria which very regularly show these involution forms have been 

 classified as belonging to quite a different order from that to which the 

 bacteria belong. The ordinary view of the involution forms is that they 

 are degeneration forms, that they correspond, in other, words- to the halt 



