216 



SCIENCE. 



[N. S. Vol. XXIII. No. 680. 



It was found that the addition of one 

 per cent, formalin to salt solution suspen- 

 sions of cultures made no difference in the 

 agglutination results, if the cultures thus 

 f ormalinized were allowed to stand for some 

 time. Freshly added formalin seemed to 

 inhibit agglutination. 



Further experiments are under way to 

 determine more exactly the action of for- 

 malin in the agglutination process. 



Note on the Thermal Death Point of B. 

 dysenterice Shiga: W. D. Frost and 

 Mart W. Swenson, University of Wis- 

 consin. 



Four different strains of B. dysenterice 

 were tested; one of the Shiga type and 

 three of the 'Flexner-Harris' type. The 

 method used was that suggested in the 

 'Procedures Recommended by the Bac- 

 teriological Committee of the American 

 Public Health Association, ' except that the 

 reaction of the medium was 0.0 on Fuller's 

 scale instead of 1.5 + and also in some 

 cases only 5 c.c. of bouillon was used in- 

 stead of 10 c.c. In the latter cases the 

 5 c.c. of bouillon after exposure was mixed 

 with an equal amount of double-strength 

 agar and plated. Exposures were made at 

 temperatures ranging from 55° to 72°. It 

 was found that the majority of the cells 

 were killed between 55° and 60°, but that 

 frequently a relatively small number, pos- 

 sibly one individual in a hundred thousand 

 or a million, may persist at much higher 

 temperatures, even 70°. The cause for 

 this wide variation in resistance to heat 

 among the different cells is apparently due 

 not to variation in the reaction of the cul- 

 ture medium, for both an alkaline and an 

 acid medium were used, nor to variations 

 in the composition of the medium, since the 

 same batch of medium was iised through- 

 out, but to some undetermined cause or 

 causes. 



A Study of the Laws Governing the Resist- ] 

 ance of B. coli to Heat: Stephen De]\I. ] 

 Gage and Grace Van E. Stoughton, ] 

 Experiment Station, Lawrence, Mass. 

 Experiments were made in which it was 

 determined that the great majority of the 

 bacteria in any B. coli culture are destroj^ed 

 by five minutes' exposure to some tempera- 

 ture between 50° and 60° C. A few indi- 

 viduals, however, in each culture will sur- 

 vive much higher temperatures, in some ; 

 cases remaining alive after exposure to 

 90° C. The very close range (about 10° | 

 C.) of temperature at which the destruc- 

 tion of the majority of the individual bac- i 

 teria occurred, as compared with the con- \ 

 siderable range (about 35° C.) in the 

 temperatures at which complete steriliza- ; 

 tion was effected, would indicate that the ! 

 determination of this majority death point 

 would be of more value in species identifi- 

 cation than is the determination of the 

 absolute thermal death point. as at present 

 employed. ■ 



Using thermal death point tests alone, i 

 this culture of B. coli would be included , 

 among the sporulating bacteria, although 

 there was no morphological evidence that 

 true spores (endospores) were produced. ,! 



Experiments were also made to deter- 

 mine whether, by successively selecting ■ 

 cultures originating from individual or- 

 ganisms which had survived temperatures 

 above the majority death point and sub- 

 mitting these cultures to the death point ^ 

 tests, a race of organisms could be propa- ; 

 gated in which the majority of the indi- i 

 viduals would be able to resist higher tem- 

 peratures than was the case with the orig- ' 

 inal culture. The experiments failed not ; 

 only to produce such a race, but the results 

 indicated the tendency toward the produc- ! 

 tion of a degenerate race whose majority 1 

 death point remained the same as for the 

 original culture, and whose absolute ther- ' 

 mal death point was reduced toward the 



