ARTHROSPORES. 67 



its use in such case being confined to the preparation of a coloured 

 slide, which, in itself, is now valueless as a criterion. 



The property of offering considerable resistance to decolorising 

 agents, possessed by the endospores, is also shared by the vege- 

 tative forms of a few species of bacteria, among which are the 

 tubercle bacilli and the leprosy bacilli. This unusual behaviour 

 greatly facilitates their detection by microscopical examination 

 alone, and is of particular utility in this respect in the examina- 

 tion of milk and of the sputa of consumptive patients. 



The differential staining of tubercle bacilli, also experimentally 

 applied to non-pathogenic bacteria by many bacteriologists, will be 

 found dealt with in each of the above-named books. 



55. Arthrospores. 



As already remarked, the capacity for forming endogenous spores 

 is not universal among the fission fungi. The question then arises 

 as to the means whereby those species not endowed with this 

 faculty protect themselves against adverse external influences. 



In many cases the resistance of such cells, and consequently 

 the maintenance of the species, is secured by the development of a 

 protective wall of cells. This is most frequently met with in 

 zoogloea-masses of bacteria. 



In other cases actual spore formation occurs. This, of course, 

 takes place not within the bacterial cell, since that would imply 

 endospore formation, but by a thickening of the membrane of the 

 individual cell in question, which thereby plays the part of a re- 

 productive cell. This procedure is known as arthrospore forma- 

 tion, since the spore detaches itself from the chain of moribund 

 cells, encysts, and becomes dormant until conditions are once more 

 favourable for its germination, when the cell increases in length 

 and subdivides in the same manner as the vegetative form. 



The thickening of the cell membrane of the incipient arthro- 

 spore proceeds, in many instances, to such an extent as to form 

 spiny excrescences on the exterior surface. This was observed by 

 HANSGIRG (I.) in two species of bacteria, viz., Mycacanthococcus 

 cellaris and Mycotetraedron cellare, found by him on the walls of a 

 cellar at the Castle of Pleissen, at Leipzig. The arthrospores of 

 the latter species, which are tetrahedral in form, exhibit at each of 

 the four angles a spiny thickening of the membrane 2 p in length. 



The name arthrospore will be understood when it is remem- 

 bered that this kind of spore is met with particularly in the thread 

 bacteria, from which it becomes, as it were, actually dismembered. 

 Examples of this are exhibited by the Crenothrix observed by 

 Cohn, Cladothrix by Zopf, Leptothrix by Miller, and Streptothrix 

 Foersteri by GASPERINI (I.). The discovery of these organs in 

 species of cocci, &c. such as the urea bacterium found by JAKSOH 

 (I.), in B. vernicosum by ZOPF (II.), in Bacterium Zopfii\>y KURTH 

 (I.), and so on was only a secondary matter. 



