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’ 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 ‘‘Beitriige zur Biologie d. Pflanzen.” 
