COHN, WOLBACH, HENDERSON, AND CATHCART 223 



The optimum temperature is about 38°C. At ordinary room tem- 

 peratures (20-24°C.) growth is very shght. 



The action on bread was studied by the inoculation of baked 

 loaves and by the incorporation of cultures in the dough. In both 

 cases the bread was incubated at 37.5°C. and examined after 24 or 

 36 hours. The rope produced by addition of the pure cultures was 

 identical in physical properties and odor with that of the bread 

 from which the cultures were isolated. 



In all instances the softening occurred just in the centers of the 

 loaves and progressed outwards. The foci of softening in bread took 

 on a brownish tint and became sticky, and particles on separation 

 yielded delicate threads of from a few inches to 6 or 7 inches in length. 

 In the case of cultures introduced with considerable amounts of 

 liquid media a cavity was produced. In bread or dough to which 

 acid was added the softening and odor were less pronounced and were 

 finally suppressed at a hydrogen ion concentration of approximately 

 10~^N. In acidities sufficient to retard the growth of the organism 

 the discoloration of the softened foci did not occur. 



The original loaf was softened and discolored, and slowly developed 

 the characteristic slimy and viscous condition. Examination of an 

 aqueous extract of a decomposed portion of this loaf with the con- 

 centration cell revealed a marked diminution of acidity, — from ap- 

 proximately pH 5.3, characteristic of normal bread, to pH 6.2. Other 

 specimens gave the following values for pH; 6.5, 6.1, 6.3. 



As a result of these observations we were led to a study of the 

 relation between hydrogen ion concentration and the growth of the 

 organism. 



Three culture media were prepared : a synthetic medium known as 

 Cohn's solution, a potato medium, and a wheat paste. These media 

 were then divided into portions, acid or alkali was added to bring these 

 to different hydrogen ion concentrations, they were sterilized, and 

 finally inoculated with a culture of the organism, or of the spores. 



The accompanying curves of the variation in hydrogen ion concen- 

 tration of these media during titration will indicate the general char- 

 acteristics of the preparations, and may perhaps serve others as a 

 basis for similar work. 



