172 IOWA ACADEMY OF SCIENCES. 



examination of both showed very few bacteria, as would be 

 expected from the dry condition. About half a gram of the 

 flours tested was placed in each of four tubes of sterile milk, 

 and four tubes of peptone bouilloQ, and allowed to remain 

 at 95*^ Fahrenheit, for twenty-four hours. The tubes were 

 then heated for thirty minutes in an Arnold sterilizer to destroy 

 all except the resistant spores. After heating, these tubes 

 were placed at 9b° Fahrenheit again for development. The 

 results were somewhat variable. Most of the tubes showed 

 the presence of a spore form capable of surviving the heating. 

 A few of the tubes showed no development after the heating, 

 indicating no spores were present. Sterile bread, in Petri 

 dishes, was then inoculated from the tubes, showing by micro- 

 scojDic examination that spores were present. From one brand 

 of flour a typical slimy bread was produced. From the other 

 brand a slight yellow coloration was produced with presence 

 of ammonia, but the typical slimy condition was not present. 

 It is unfortunate that more samples were not examined, but 

 from the observations made it is evident that the flour may 

 act as a source of contamina'^ion, but that the number of 

 bacteria in a given amouat of flour is probably small. 



YEASTS. 



The common dry caka yeasts to be purchased in Ames were 

 examined in the same manner as the flour. 



Yeast foam. — Used very largely in Ames, and in several 

 cases where spoiled bread had occurred, microscopic exami- 

 nation showed, besides the yeast cells, four forms of bacteria, 

 indicating at least that many spacies, and also a numbar of 

 spores. Produced typical slimy colored decomposition on ster- 

 ile bread. 



Yeast loafers. — Microscopic examination showed two distinct 

 forms of bacterial cells, also spores. Produced typical odor 

 on sterile bread. Entire surface covered with a slightly 

 wrinkled, pinkish growth, very viscid. Threads four feet 

 long, forming from one spot when touched with a needle. 



On time yeast. — Used in some cases of spoiled bread. Micro- 

 scopic examination showed bacteria numerous; produced slimy 

 fermentation on sterile bread; very large bacilli, together with 

 smaller ones, present in every sample examined. 



Fleischman's compressed yeast. — Microscopic exanaination 

 showed large bacilli present, but no spores observed. In 



