1894. J NEW-YORK MICROSCOPICAL SOCIETY. 5 



teria nlm, perhaps to any degree, must cause such contraction of 

 the sensitive plasm within the cells and of that connected with 

 the cilia as to involve just this known resistance to coloration. 

 In several recent investigations there has been a return to simple 

 processes by which, without drying or heating, the living bacteria 

 have been successfully stained throughout, including the cilia ; 

 for example, that of N. Sjobring,' who, in studies of their structure 

 and nuclei, used nitric acid as fixative, stained with carbol-meth- 

 ylen-blue or carbol-magenta-red, decolorized with nitric acid, 

 and examined in glycerin and water ; that of Straus,^ who merely 

 added diluted Ziehl's solution to a loopful of bouillon culture of 

 several kinds of spirilla ; that of Klein,' who used, on the living 

 spirillum of Asiatic cholera, a mixture of equal parts of absolute 

 alcohol and a solution of gentian-violet in anilin water, during 

 five to ten minutes ; and that of R. L. Maddox,* who used satu- 

 rated solution of tannic acid as fixative, and then added a satu- 

 rated solution of iron sulphate, containing about two per cent of 

 citric acid, for the staining of spirilla. Not only, therefore, is it 

 certain that the process of drying and overheating bacteria on 

 thin covers long delayed the discovery of cilia and other details 

 and is yet impeding their investigation, but it is probably responsi- 

 ble for some of the varying conclusions of modern workers con- 

 cerning distribution of chromatin, septa, nuclei, spores, and cilia 

 through artificial and false structures developed by contraction. 



To recapitulate, the new steps suggested by these considera- 

 tions, when it is thought desirable to prepare a dried bacteria film, 

 are as follows : preliminary dilution of a droplet of the bacterial 

 growth in sterilized distilled water ; killing and fixation of the 

 bacteria, in a drop upon a thin cover, by addition of suitable fixa- 

 tive ; slow evaporation at a low temperature ; and immersion in 

 a mordant before staining. 



As to the selection of fixative, I have tried weak aqueous solu- 

 tions of the following reagents, in succession or in comparative 

 series, during the recent preparation of two hundred and thirty 

 mounts of several species of ciliated bacteria, spirilla of Beggiatoa, 

 spirilla undula, etc. As the fixative cannot be removed from 



1 Centralbl. f. Bikt. u. Par., xi. C189O1 65- ' Idem, xiv. (1893), 257. 



^ Idem, xiv. (189O. 618. < Jour. Roy. Mic. Soc. (1893), 718. 



