300 PHYSIOLOGY OF BACTERIA 



than the preceding one. With the fifth culture, Magoon suddenly 

 changes his technique and holds the culture for sixty-four days 

 instead of twenty-nine as in all previous experiments. The result 

 is a greater resistance. If we do not use these incomparable last 

 data, but consider the last experiment finished after twenty-nine 

 days (Magoon's records make this possible), then it becomes evident 

 that the fifth culture is decidedly less resistant than the fourth, 

 and about equal to the third. The experiments do not prove an 

 increase in resistance by selection, but, on the contrary, a fluctuation. 

 The last survivors are not more resistant than the average. 



Similar are the experiences of Arnold (1929) who sprayed several 

 millions of cells of Bad. coli and Bad. prodigiosum into the nose, 

 made cultures of the few remaining cells and repeated the experiment 

 with these cultures as often as nine times. "There was no evidence 

 of an acquired resistance on the part of those bacteria that had sur- 

 vived for a maximum period of time upon the nasal mucosa." 



More than twenty years previous to this experiment, Gage and 

 Stoughton (1906) tested Baderium coli. Broth cultures of this 

 organism were exposed for five minutes to temperatures ranging 

 from 45°C. to 100°C. The survivors of each tube were counted 

 by plating. The tube heated to 60° was used as the ''second genera- 

 tion." Subcultures of it were again exposed to different tempera- 

 tures, the survivors were counted, and the culture heated to 60° 

 was used as "third generation." In this way, nine generations 

 were tested, all of which had been heated to 60°C. or 55°C. The 

 results are shown in Table 86. The numbers are the survivors in 

 percents of the inoculum; -j- means growth in the tube, but no 

 colonies on the agar plate; means no growth in the tube. 



Gage and Stoughton summarize their results as follows: "Experi- 

 ment 195 in which we attempted to produce, by the survival of 

 the fittest, a race of especially resistant organisms, demonstrated a 

 diametrically opposite result." 



This agrees with the experiences of Gates (1929) whose experi- 

 ments on death by ultraviolet light will be recorded on p. 372. He 

 states that "cocci from colonies of the last surviving organisms 

 have proved to be inherently no more than normally resistant to 

 ultraviolet light." 



These experiments speak quite decidedly against the 

 assumption that the last survivors are more resistant; 



