A Typhoid Bacteriophage. 



163 



The most striking single fact about these lytic principles is 

 that they are only active when added to young growing cultures. 

 I obtain the best results in lysis experiments where I wash up the 

 growth of a young agar culture in broth and then add enough of 

 this heavy emulsion to 10 c.c. of sterile broth tube to make it 

 definitely cloudy. A large amount of unused culture fluid media 

 media favors the reaction enormously. I have tried adding drops 

 of a heavy young typhoid emulsion to a freshly dissolved trans- 

 parent culture until it is again turbid, but the lytic principle which 

 can be demonstrated to be active on other turbid young broth 

 cultures in a dilution of 1-100, will be unable to dissolve 0.2 or 

 0.3 c.c. of a young typhoid emulsion in 10 c.c. of lytic principle 

 unless fresh nutritive material is added. 



Another extremely important fact about this lytic principle 

 (similar observations have been made by other workers), is that 

 one single contact with the lytic principle is sufficient to divide a 

 normal culture into two types, one the typical colony, the other 

 atypical carrying the lytic property. This can be demonstrated 

 both in fluid and in solid media. If the lytic principle is added 

 in a dilution of 1-10 to a turbid culture, and the culture is shaken 

 and plated immediately, the two types, in some instances, will 

 be obtained. If an active filtrate is allowed to drop on a young agar 

 growth of typhoid, the culture will be dissolved at this point, and, 

 if the plate is incubated for another day, a few lytic colonies may 

 develop in this area. The so-called resistant bacilli must be 

 present in the original culture, together with the susceptible 

 bacilli, since, in the case where the broth culture is plated imme- 

 diately, the resistant bacilli have not had time to become hardened 

 to the action of the lytic principle. 



The above findings have simply been enumerated without any 

 attempt to develop a theory. The data on the subject is still 

 accumulating too rapidly for me to take definite sides. 



