A Typhoid Bacteriophage. 161 



transparent after several hours incubation, whereas, the latter, 

 except in rare instances, failed to clear up. The few cases where 

 the addition of "appearances" to the turbid broth cultures seemed 

 to exert a dissolving action can, in my opinion, best be interpreted 

 as lytic colonies almost completely dissolved, but which still 

 contained a small number of living bacilli carrying the lytic 

 principle. All attempts to find a definite structure in the "ap- 

 pearances" by different methods of staining have failed. Plates 

 have been observed at frequent intervals, to see if the amount of 

 "appearance" increased, but this was never the case. Whether 

 the "appearances" do not increase because the lytic principle 

 dissolves up all the susceptible bacilli present as fast as they grow, 

 and reduces them to " appearances," and has no action on the so- 

 called resistant bacilli which form the bulk of the lytic colony, 

 is still to be determined. On the other hand, it might be argued 

 that the "appearances" do not spread on further incubation be- 

 cause by that time the typhoid bacilli have grown too old to be 

 susceptible to the action of the lytic principle. From my obser- 

 vations to date, although very incomplete, I have found nothing 

 to indicate that these "appearances" represent living structures, 

 they suggest much more that the same phenomenon which is 

 indicated by the clearing of the broth when the lytic principle is 

 acting in fluid media occurs also on solid media. 



It seems possible to me that when a fluid culture is rendered 

 transparent it means that the susceptible bacilli present in the 

 originally turbid emulsion are reduced to the state of "appear- 

 ances." A chemical analysis of the end product of the dissolved 

 culture compared with a similar analysis of the "appearances" 

 if they can ever be obtained in sufficient quantity, ought to prove 

 this point. I have experiments of this nature planned at the 

 present time. 



The potency of this lytic principle has not increased from one 

 generation to another as indicated by d'Herelle in certain instances 

 but has remained the same over a period of three months. The 

 original stool filtrate, dissolved culture derivatives, derivatives of 

 broth fishing of lytic colonies all appear to be about equally active. 

 I have carried out experiments to see whether the potency of 

 the lytic principle depended to any extent on the amount of 



