196 TECHNOLOGY OF BACTERIA. 



The difficulty of obtaining satisfactory photo- 

 micrographs of the smallest micro-organisms is 

 illustrated in Figures 3 and 6, Plate XL These 

 represent the best results which the writer has 

 been able to attain from a large number of trials 

 in photographing the tubercle-bacillus. In Fig. 3 

 there are six of these bacilli, included within an 

 epitheloid cell, from a specimen of the sputum of 

 a tuberculous patient. The specimen is well stained 

 with fuchsin by Ehrlich's method ; and under the 

 microscope the outlines of the cell, with its nucleus 

 and the deeply-stained bacilli, are seen very dis- 

 tinctly. But in the attempt to photograph this 

 object it was found to be impossible to bring all 

 of the bacilli into focus at the same time ; so that, 

 while two bacilli are seen with tolerable distinct- 

 ness, the others, being a little out of focus, can 

 scarcely be distinguished. Fig. 6 represents the 

 best result I have been able to obtain in photo- 

 graphing a single bacillus from the same source, 

 stained in the same way, with fuchsin. A close 

 inspection will show that this bacillus is formed 

 of a chain of four oval spores. When it is re- 

 membered that this is magnified 1,000 diameters, 

 and has been stained and mounted secundum artem, 

 it will not appear surprising that this minute ba- 

 cillus escaped observation for so long a time. 1 



1 In remodelling the plates for the second edition of this work, the 

 photo-micrographs above referred to have been omitted, and we give in 

 place of them a reproduction of some of Koch's beautiful illustrations 

 (chromo-lithographs, Plate IX.), which will no doubt be found more 

 satisfactory. 



