IOWA ACADEMY OF SCIENCES. 171 



first noted by J. L. Hamilton.* In the first trial, the tempera- 

 ture at the end of one hour's baking was 196° Fahrenheit. 

 Fiva minutes later it reached 206 -', then gradually declined to 

 150°, within two hours. In the second trial the temperature 

 recorded at the end of baking was 197°, which raised to 208° 

 within five minutes, and within fifteen minutes sank to 200° 

 Fahrenheit and reached 150° in about the same time as in the 

 first trial. 



These results are practically the same as found by Dr. 

 Russell, who says at no time is the temperature of baking high 

 enough to kill the spores of the potato bacillus. The same 

 applies to the Bacillus liodermos and shows that if either of 

 these bacteria find their way into the bread during the process 

 of bread making, the baking will not destroy them and under 

 favorable conditions of temperature as found during the hot 

 weather of summer, they may develop very rapidly. 



HOW THE BACTERIA GET INTO THE BREAD. 



In considering how the bacteria came into the bread the 

 following were considered as possible sources of contamina- 

 tion: 



First. — From the air or from water or milk used. 



Second. — From the addition of potatoesor potato water to the dough. 



Third. — Prom infected flour. 



Fourth.— From impure yeast. 



The natural habitat of Bacillus liodermos, as far as literature 

 on the subject shows, has not been ascertained. It has been 

 found in milk by Loeffler and in spoiled bread. The potato 

 bacillus occurs at times in milk and being a soil organism may 

 accur in water and possibly in the air. The sources mentioned 

 under number one while possible, seem hardly a probable 

 source of contamination in many cases unless the water or 

 milk used be decidedly impure. 



The use of potatoes might readily carry over large numbers 

 of the potato bacillus even if the portion used had been boiled. 

 Some of the cases of slimy decomposition occurred where no 

 potatoes had been used, so this is not at least a necessary 

 contamination. 



EXAMINATION OF FLOUR. 



Two brands of roller process wheat flour were examined to 

 determine if contamination be from that source. Microscopic 



*The Lanoet (London), 1894 December 8, Abstract, Experiment Station Record, 

 Vol. VII, P. 793 



