DISTINCTIVE CHARACTERS OF THE BACTERIA. 181 



threads without a sheath, cells with sulphur granules ; inha- 

 bitants of water. Phragmidiothrix, threads without sheaths, 

 successive divisions very extensive ; cells free from sulphur ; 

 inhabitants of water. Leptothrix, threads with or without 

 sheaths, divisions not very extensive ; cells devoid of sulphur. 



4. Cladothrix. Show coccus, rod, thread, and spirillar 

 forms. The thread form is provided with pseudo-branches. 

 Spore formation not demonstrated. Genus : Cladothrix. 



A priori the possibility of the mutability of form of the Disadvan- 

 bacteria asserted by Zopf, and to which expression is given in |" ^ e 

 the foregoing classification, must at any rate be admitted ; adoption of 

 but before we accept it as a matter of fact, and as so general, ]^ n yp- 

 we must demand complete proof, and we must insist the more 

 strenuously on a satisfactory proof, as we Avould be deprived, 

 by the admission of extensive changeability of form, of an 

 important diagnostic aid which is of great value to us in 

 medical and hygienic practice. We know now a number 

 of exciting agents of disease which occur, for example, in the 

 form of characteristic bacilli ; we are able to make a diagnosis 

 of tuberculosis by the discovery of the tubercle bacillus, and 

 of cholera by the demonstration of the cholera bacilli. If the 

 characteristic bacilli are absent on careful and repeated in- 

 vestigation, and if we find only bacilli or cocci of other form, 

 we consider ourselves justified in denying the existence of 

 tuberculosis or of cholera. Further, we frequently undertake 

 the investigation of some object, which is suspicious from a 

 hygienic point of view, for the presence of typhoid bacilli, of 

 anthrax bacilli, &c., and we can only hope for a result because 

 we search in all cases for an organism of definite and charac- 

 teristic form. If, however,' Zopf's view is correct, and if these 

 bacilli often occur in a coccal form, investigations of this 

 kind must obviously be without result ; it is impossible to 

 recognise by the microscope organisms in the coccal form, and 

 hence any extraneous innocent coccus might lead us to the 

 diagnosis of tuberculosis or typhoid fever just as well as the 

 supposed coccal form of these pathogenic bacilli. We should 

 also meet with great difficulties in isolating organisms by 

 cultivation if the colonies of, for example, the typhoid bacillus 

 could occasionally contain only coccus forms. We should 

 then find it very difficult to decide with regard to a group of 

 cocci whether they should be included in the genus spirillum, 

 or beggiatoa, or micrococcus, or bacterium, and also to what 

 species of these genera they belonged. 



Complete proof of the accuracy of Zopf's views has certainly Absence of 

 not been furnished with regard to the great majority of the univerfa? 10 

 fission fungi. Our most skilled microscopists and bacteriolo- applicability 



gists have never as yet been able to demonstrate a trans- ?* Zo Pf 8 - 



hypothesis. 



