PLEOMORPHISM : INVOLUTION 



25 



vibrio, nor spirillum forms appear. The various twistings and distortions of 

 filaments, and aggregations of motionless gonidia, which have been described 

 as phases of pleomorphic development, are quite fortuitous. 



Pus-cocci (Staphylococci) may be cultivated in any number of different 

 media, but they appear with unalterable persistence in the form of little 

 spheres (Fig. 28, a). The cholera vibrio occurs in the form of a slightly 

 curved rod, and it occurs in this form only. The only observable variation 

 in growth is that in some cultures isolated cells may prevail, and in others 

 chains (Fig. 28, k). In a hay-infusion culture of B. subtilis, for instance, 

 we meet side by side motile and motionless single cells (Fig. 13, a, b), 

 and, especially in the surface pellicles, motile 

 and motionless chains (Fig. 13, b). In all these 

 the individual bacterium remains unchanged, a 

 unicellular, peritrichous-ciliate, actively motile 

 rod (Fig. 13, a). The motionless rods arise 

 from any causes which bring about temporary 

 paralysis of the cilia, and the motile chains 

 from the clinging together of successive genera- 

 tions of cells. In a fresh culture the fluid is 

 uniformly turbid, with actively moving isolated 

 rods only. These are afterwards driven by 

 lack of oxygen to the surface of the culture, 

 where they grow out into long, motionless, 

 spore-bearing chains devoid of cilia, the aggre- 

 gation of which forms a membrane or pellicle 

 on the surface of the liquid. This completes 

 the cycle of forms. 



These instances will suffice to show that 

 pleomorphism in its true sense does not exist. 

 (haplo-bacterid) the 'growth-form ' only changes, 

 clusters, or zoogloea, according to the substratum they live in, but the 

 form of the individual of the vegetative cell remains the same. 



That proper and improper nutriment must have a great effect upon 

 the size of the cell is evident. Giant and dwarf forms occur among the 

 bacteria as among all other organisms, and have the same significance. 

 But for all species of bacteria there is an average size and form, deviations 

 from which are not more extensive than they are among other organisms : 

 always assuming that the conditions of existence are suitable, that the 

 bacteria are in a healthy condition, which is far less frequently the case than 

 we are apt to think. Imagine a few thousand animals cooped up together 

 in a confined space, plentifully supplied with food, but without provision for 

 the removal of their dejecta. A few hours would suffice to bring about 

 a frightful state of things. And these are just the conditions under which 



Fig. 12. Cladothrix dicholoma, 

 formation of swarm spores. The 

 sheath (stippled) of the left branch 

 has opened and gives exit to a swarm 

 spore; in the right branch a whole 

 group of cells has changed into swarm 

 spores, each with a lateral tuft of cilia. 

 On this side too the sheath is swollen 

 up, loosened. Magn. iooo. 



In all the simple bacteria 

 Single cells unite to chains, 



