VARIOUS GROWTH-FORMS OF BACTERIA 39 



and Bean family). These belong to a species called Bacillus radi- 

 cicola, and the mode of their production will be discussed when we 

 come to treat of the Nitrogen bacteria to which they belong. The 

 normal form is that of a short rod, but the involution forms are like 

 those exhibited in Fig. 58, in which we see that some of the cells 

 are branched whilst others exhibit irregular swellings. Fig. 59 repre- 

 sents Spirillum giganteum showing this feature, and other examples 

 may be easily seen in Bac. tuberculosis, Bac. diphtheriae, and a large 

 number of other bacteria. That they are unhealthy structures may 

 be demonstrated by staining with methylene blue or one of the other 

 stains of this class, when it will be seen that the inside of the involu- 

 tion forms are only faintly or not at all coloured, showing absence of 



c^ 



%. 



Fig. 58. — Bac. radicicola. Fig. 59.— Spirillum giganteum. 



Involution forms. Involution form. 



protoplasm. Again, if the species is one like Spirillum giganteum 

 that shows a large quantity of reserve material, it will be found that 

 the involution forms are almost entirely devoid of this material. They 

 never divide or show any signs of life, and may be regarded as indi- 

 viduals which are either dead or dying. There is no doubt that the 

 line separating structures included under morphological variations and 

 involution forms, is not sharply defined. Whilst the researches of 

 Hansen on Bac. aceti and Bac. Kiitzingianum have shown that in 

 these species fantastically shaped cells were not unhealthy, for divi- 

 sion took place in them, in the majority of forms it may be assumed 

 that distortion and unhealthiness go hand in hand. 



§2. PHYSIOLOGICAL VARIATIONS. 



The descriptions of the variations in the first paragraph of this 

 chapter were concerned with changes of form. There are, however, 

 bacteria, which, although belonging to the same species, and outwardly 

 quite similar, show a great variety in their physiological characteristics, 

 that is, their functions are not all alike. Thus, one culture will liquefy 

 gelatine, another culture of the same species, with a different past, may 



