On the Ajipearances, <&c. By G. F. Doivdeswell. 33 



cholera is dried and stained with an alcohohc solution of eosin, and 

 suhsequently with a nuclear stain, the characters of the microbe 

 again appear totally difi'erent. The eosin stains the plasma of the 

 blood, as also the stroma of the red corpuscles, leaving the sub- 

 stance of the " capsule " of the microbe unaltered ; this appears 

 white on a coloured ground, and of a considerable size. The 

 nuclear stain colours the plasma of the cell of the microbe, but 

 from some cause not yet evident it appears materially reduced in 

 size, shrunk to a mere speck, totally unlike the body shown in 

 preparations stained by the former method (figs. 2 and 3). 



This appearance of a " halo " or capsule has been regarded in 

 very different ways by different observers ; some have considered it 

 as merely an optical appearance, due to refraction and having no 

 objective existence ; others again as a specific character of particular 

 microbes. From the preparations here shown it is evident that it 

 has a substantial existence, but the fact that in the same organism 

 it is visible under some conditions and in others not, proves that 

 without further careful investigation it cannot be regarded as a 

 specific character. It is probably mucoid or gelatinous ; in un- 

 stained preparations its visibility no doubt depends upon its being 

 of higher refrangibility than the surrounding medium, as in the 

 blood-plasma ; in dried preparations mounted in Canada balsam it 

 is not apparent, either when unstained or stained by aqueous solu- 

 tions of the usual anilin dyes ; but is conspicuous as above described 

 when an alcoholic solution of eosin is employed. In this case the 

 reagent seems to have altered the whole character of the cell, as is 

 seen by comparing the first and second, and the third and fourth 

 preparations. 



I lately obtained a cultivation of the virus of this disease, for 

 which I have to thank Mr. W. Watson Cheyne, and have found on 

 examination that morphologically the microbe is identical with that 

 of the so-termed Davaine's septichasmia in rabbits above referred 

 to, the slight modifications in form and size which it exhibits in 

 difi'erent conditions being merely the variations which most, or 

 probably all, species of the lower fungi are liable to under difi'erent 

 conditions of nutrition, or sometimes, to all appearance, spon- 

 taneously. In blood of the fowl or pigeon it is nearly of the same 

 size in breadth (0*5 //-) ; it developes, however, to a somewhat 

 greater length in the majority of the cells, to five or six times this 

 size (fig. 4). 



I had previously described * the microbe of Davaine's septi- 

 chaemia in rabbits as a Bacterium, to the characters of which 

 genus as defined by Cohn it seemed most nearly to correspond, 

 as it occurred in the blood in these cases, but few cells being found 

 in the organs and other tissues. Subsequently, however, I found 



* Loc. cit. 

 Ser. 2.— Vol. VI. D 



