CHAPTER IV. 



VEGETATIVE REPRODUCTION BY FISSION. 



42. Division in One Direction. 



IN order to reproduce by fission in one direction, the cell becomes elongated, 

 and a partition (septum) is developed in the interior of the cell at right angles to 

 the length. This septum then divides into two lamellse, thus effecting the 

 separation of the daughter- cell from the mother-cell. If the organism is living 

 under conditions favourable to its vitality, each of these cells will soon undergo 

 a similar process of division. In many instances the new-formed cells of the 

 second, third, fourth, &c., generations do not become entirely 

 detached, but remain connected one with another ; and if as 

 is most often the case the division takes place continuously in 

 the same direction, chains of cells are formed. When the 

 / members composing the chain consist of cocci, the fission 

 fungus is frequently designated a streptococcus, instead of 

 merely coccus. Hallier and Itzigsohn proposed to apply the 

 term Mycothrix to these rosaries of cocci. When the mem- 

 bers are united chiefly or exclusively in pairs, the organism 

 is termed diplococcus ; and such of the cocci as incline to 

 no Bacillus g rou P themselves in grape-like agglomerations are frequently 

 tuuiescens. designated, in medico-bacteriological literature, by the name 



a and 6, chains of short staphylococcus, first bestowed on them by OGSTON (I.) in 



members. (After A. jgg o 



agn.noo. jj. ^ e mem bers of a chain are not iso-diametric cocci, 

 but rods, they are mostly termed thread (filamentous) cells, of which the hay 

 bacillus affords an excellent example. 



In an iso-diametric cell, the separation of the new cells and therefore the 

 preliminary expansion of the mother-cell may occur in one of two directions : 

 either lengthwise or crosswise, the former case wherein the position of the 

 dividing septum is transverse, i.e. perpendicular to the longitudinal direction 

 being the most usual. On the other hand, only a few examples of the second or 

 longitudinal separation are as yet known. One of them is afforded by the 

 Bacillus tumescens, discovered by ZOPF (I.), which will nearly always be found 

 infesting slices of boiled carrot, when the latter are left to themselves for some 

 time in a not too damp condition. According to the conditions of vitality pre- 

 vailing, this microbe develops either chains of long ctlls formed by transverse 

 fission, or cell bands the members of which are short and joined broadside on, 

 the attached sides measuring 2.1 p each, whereas the length of each is only 1.3 /*. 

 This microbe, therefore, exhibits both styles of fission. On the other hand, 

 longitudinal fission alone is manifested in a fission fungus discovered by METSCH- 

 NIKOFF (I.), and named Pasteuria ramosa, which grows in the ventral cavity of 

 certain water-fleas (Daphnia pulex and D. magna), where it produces a fatal 

 disease. In these microbes the new septum is always longitudinal. 



In the separation process now under consideration, wherein the division 

 of the mother-cell and the casting off of the daughter-cell take place in one 



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