CH. X. — MORPHOLOGY OF THE BACTERIA. — ARTHROSPOROUS BACTERIA. 469 



morphological investigation. The other genera are distinguished by the difference in 

 their conformation. 



Leuconostoc mesenterioid.es, the ' frog-spawn' of sugar-factories, consists in the 

 vegetative state of coiled rosary-like chains of small round cells inclosed in firm sheaths 

 of mucilage, and accumulated in great numbers into large compact gelatinous masses 

 (' zoogloeae '). Many of the cells perish at the close of the vegetative season when the 

 nutrient substratum is exhausted. Single cells of the rows, disposed at irregular 

 intervals, become somewhat longer than the rest and have a thicker wall, and their 

 contents are apparently denser and more highly refringent. They are at length set at 

 liberty by the dissolution of the mucilage, and they devefope in a fresh nutrient 

 solution into new rosary-like chains resembling the parents. 



Arthrobacterium (Bacterium) Zopfii is the name given by Kurth to a species 

 which was originally found in the intestinal canal of fowls, and which vegetates at first 

 in the form of small rods when placed on a fresh nutrient substance. If the 

 substratum is solid, gelatine for instance with meat-extract, the rods remain connected 

 together and form long filaments, often with intercalary spiral coils and knots ; in a 

 fluid substratum short resting filaments are formed at high temperatures only, and at 

 20 C. the rods separate and swarm. When the nutrient substratum is exhausted the 

 filaments and rods break up into isodiametric members, cocci, which do not them- 

 selves divide again, resist unfavourable external agencies, and develope into rods or 

 filaments if supplied with fresh nutriment ; they may therefore be termed spores. 



A similar course of development is described by Zopf in the case of Arthro- 

 bacterium (Bacterium) merismopoedioides, a species which vegetates in muddy 

 water; it is complicated however by the circumstance that the isodiametric cocci which 

 are the product of the disruption of the rods do not pass into a state of rest, but after 

 swarming for a time lie without motion on the surface of the water ; then they divide 

 first in one and then in two directions which cross one another alternately at right 

 angles, and arrange themselves in flat tabular gelatinous expansions in a manner 

 corresponding to the divisions. If the cocci are now placed in a fresh portion of 

 muddy water they will again develope, after swarming for a brief time, into rods or 

 filaments. 



Crenothrix, Cladothrix and Beggiatoa are closely comparable in their develop- 

 ment with the preceding species, but they appear to exhibit a greater variety of 

 growth-forms. The agreement consists in the copious and uniform multiplication of 

 the coccus-form, which is alternately aggregated into zoogloeae or is free and even 

 motile ; the cocci are the product of filaments and rods and may develope into them 

 again. The greater complication of the cycle of forms is due to the assumption by 

 portions of the filaments and rods of the form of motile spirilla, and to their multiplying 

 abundantly in this form. The return from the spiral to the straight forms has, as far as 

 I know, never been observed. The following brief description from Zopf may assist 

 in the understanding of these species. 



Crenothrix Kiihniana (Fig. 196) is a Schizomycete which occurs frequently in 

 water containing some amount of organic substances, and sometimes in quantities 

 which are dangerous to health. Its cocci a are spherical in shape and 1-6 n in size. 

 They multiply by successive bipartitions and in so doing are united into zoogloeae 

 (/, g), which grow from microscopic minuteness to more than a centimetre in size and 



