32 Transactions of the Society. 



V. — On the Appearances which some Micro-organisms present 

 under different conditions, as exemplified in the Microbe of 

 Chicken Cholera. 



By a F. DowDEswELL, M.A., RE.M.S., F.L.S., &c. 



(^Eead IBth January, 1886.) 

 Plate VI. 



The importance of understanding the conditions under which 

 variations may appear in the morphological characters of a micro- 

 organism is obvious, as without such a knowledge correct specific 

 diagnosis is impossible. 



A conspicuous example of this is afi'orded by the microbe of 

 chicken cholera, a disease chiefly known from the accounts given of 

 it by Toussaint and Pasteur. The organism has been described by 

 the latter as a micrococcus of a figure-of-8 form, surrounded by a 

 " petit halo " ; and such is a correct description of its appearance 

 under certain conditions, with moderate amplification, up to say 

 800 diameters, and ordinary illumination. In a preparation dried 

 and stained in the usual method, e. g. with an aqueous solution of 

 methyl-violet, these appearances are changed ; there is no " halo," 

 outer envelope, or capsule ; though with the same power (800) the 

 "dumb-beU" or "figure-of-8" form remains (plate YI. figs. 1 and 5), 

 but when we come to employ higher powers (2000 diameters and 

 upwards), and especially more perfect methods of illumination, these 

 appearances in the form of the cells in the same preparation are 

 found to be deceptive. It is seen that they are mostly uniformly 

 cylindrical ; the apparent constriction of the cell- wall which gives 

 the dumb-bell form has in most cases no existence (fig. 4). It is 

 the plasma of the cell, which is aggregated chiefly at the ends and 

 which stains deeply, that gives this appearance, as I have already 

 described * in the case of the microbe of Davaine's septichaemia. 



If, however, a preparation of blood from a case of chicken 



EXPLANATION OF PLATE VI. 



Figs. 1 and 4. — From the same preparation X 800 and 2000 respectively, 

 showing the miorohe in the blood of the pigeon, dried, and stained with an aqueous 

 solution of gentian-violet. 



Figs. 2 and .S.— From another preparation x 800 and 2000 respectively, 

 showing the microbe in the blood of the same case as figs. 1 and 4, but stained 

 with an alcoholic solution of eosin, and then with a nuclear stain. 



Figs. 5 and 6. — The same microbe in the blood of a rabbit, stained with an 

 aqueous solution of gentian-violet. 



References to all the figures : — A, red, and B, white blood-corpuscles. The 

 smaller bodies are the microbes. The larger figures are di-awn with the camera 

 lucida. 



* See this Journal, ii. (1882) p. 310, and Quart. Journ. Micr. Sci, xxii. (1882) 

 p. 66. 



