barber: heredity in certain micro-organisms. 23 



before plating. In a third, exposed to dry heat two days at 

 37° C, and later brought for a very short time to 50° C, 

 both new race and check produced colonies, but the new race 

 formed them in much greater numbers. Of the five other 

 dry-heat experiments, the new race showed the better growth 

 in four, but the difference was not great. In one, a two-day 

 glycerin agar culture heated six and one-half hours at 43° C. 

 to 45° C, the check showed five colonies, the new race none. 



In several moist-heat experiments no growth occurred in 

 either. For instance, no cells survived a temperature of 64° 

 C. to 67i° C. for seven minutes in one experiment, or 70° C. 

 for twenty seconds in another. In three moist-heat experi- 

 ments growth occurred. In one, a thirteen-day glycerin agar 

 culture heated in gelatin seven minutes at 54i° C. to 57i° C, 

 the new race formed colonies while the check formed none. 

 In a second experiment, in which a four-day culture was 

 heated in glycerin agar to 55° C, there were two series of 

 tubes, one exposed to the high temperature five minutes, the 

 other ten minutes. In both series the new race colonies ap- 

 peared more abundantly and earlier than in the check. In 

 the ten-minute series only two colonies appeared in the check 

 and these very late. In a third experiment, seven minutes 

 in gelatin at a temperature of 50° C. to 53° C, both types 

 formed colonies, but the new race produced the greater 

 number. 



Summarizing the positive experiments of both series, we 

 find six in which the new race surpassed the check to a 

 marked degree, four in which it surpassed but slightly, and 

 one in which the check showed the better growth. These re- 

 sults indicate that the new race has a somewhat greater re- 

 sistance to heat and drying than the type, in spite of the fact 

 that spore production is greater in the type. As is known, 

 however, yeast-cells not in the spore state may go into a very 

 resistant condition, and it may be such cells which enable 

 the race to withstand the unfavorable conditions. Micro- 

 scopical examination of the roll cultures showed that only a 

 small per cent, of the cells of either type survived. 



As regards the liquefaction of wort gelatin, I have the re- 

 sults of but one experiment. The type and a new race about 



