XII. 

 PHOTOGRAPHING BACTERIA. 



WELL-MADE photomicrographs are unquestionably superior to 

 drawings made by hand as a permanent record of morphological 

 characters. This being the case, bacteriologists would no doubt re- 

 sort to this method more generally but for the technical difficulties 

 and the time and patience required in overcoming these. Koch, in 

 his earlier studies, gave much time to photographing bacteria, and 

 with very remarkable success. In his work on "Traumatic Infec- 

 tive Diseases " (1878) he says : 



"With respect to the illustrations accompanying this work, I 

 must here make a remark. In a former paper l on the examination 

 and photographing of bacteria I expressed the wish that observers 

 would photograph pathogenic bacteria in order that their representa- 

 tions of them might be as true to nature as possible. I thus felt 

 bound to photograph the bacteria discovered in the animal tissues in 

 traumatic infective diseases, and I have not spared trouble in the 

 attempt. The smallest, and in fact the most interesting bacteria, 

 however, can only be made visible in animal tissues by staining 

 them and by thus gaining the advantage of color. But in this case 

 the photographer has to deal with the same difficulties as are expe- 

 rienced in photographing colored objects e.g., colored tapestry. 

 These have, as is well known, been overcome by the use of colored 

 collodion. This led me to use the same method for photographing 

 stained bacteria, and I have, in fact, succeeded, by the use of eosin- 

 collodion, and by shutting off portions of the spectrum by colored 

 glasses, in obtaining photographs of bacteria which had been stained 

 with blue and red aniline dyes. Nevertheless, from the long ex- 

 posure required and the unavoidable vibrations of the apparatus, the 

 picture does not have sharpness of outline sufficient to enable it to be 

 of use as a substitute for a drawing, or, indeed, even as evidence of 

 what one sees. For the present, therefore, I must abstain from pub- 

 lishing photographic representations ; but I hope, at a subsequent 

 period when improved methods allow a shorter exposure, to be able 

 to remedy this defect/' 



1 The paper referred to is published in Cohn's "Beitrage zur Biologic d. Pflanzen." 



