io Lectures on Bacteria. -[$ IT. 



The straight rod-forms (Figs, i, 2) have received the special 

 name of rods, Bacteria, from the earlier writers. Short or long 

 rods and other terms are obvious designations for subordinate 

 peculiarities of shape, but have no other value. 



The screw or cork-screw forms are termed Spirilla, Spiro- 

 chaetae. Those which are only slightly curved, that is, which 

 form a portion only of a turn of the screw, being intermediate 

 between the two preceding categories, have been called by Cohn 

 Vibriones in accordance with the nomenclature of older authors. 

 It is well that we should understand clearly that these and other 

 names, which will be mentioned presently, are only used to define 

 the shapes of the organisms. It would indeed be better to give 

 them proper names expressive of their outward appearance, 

 and to use terms like sphere, screw ; and it is to be hoped 

 too that the jargon which prevails at present, especially 

 in medical literature, will gradually be replaced by a rational 

 terminology. 



The cocci and rod-forms are sometimes liable to a peculiar 

 deviation from their ordinary shape ; single cells, lying between 

 other cells which remain true to one of the typical forms 

 described above, swell into broadly fusiform or spherical or oval 

 vesicles several times larger than the typical cells. This has been 

 observed in species of Bacillus, Cladothrix, &c., and with special 

 frequency in the Micrococcus of mother of vinegar. There is 

 some ground for assuming, though further proof is required, 

 that these swollen forms are the products of diseased develop- 

 ment, indications of retrogression and involution, and they were 

 therefore termed by Nageli and Buchner involution-forms (see 

 Fig. io). 



2. According to the nature of the union or want of union of 

 the cells, we must first of all distinguish between the forms in 

 which genetic union and arrangement is maintained after succes- 

 sive bipartitions, and those in which it is severed or displaced. 



When the cells continue united together in the connected 

 sequence of the divisions we have 



