BACTERIOLYSIS 27 



1. All three tubes are turbid. From such a result it may not 

 be concluded that an active bacteriophage is not present, for if 

 a complete lysis of the bacteria is taken as the only criterion for 

 determining its presence the bacteriophage will, in a majority of 

 cases, be overlooked. Lysis is but a single fact in the midst of 

 a very complex group of phenomena. If the three tubes are 

 turbid take about 0.02 cc. from each of the tubes by means of a 

 platinum loop and spread over the surfaces of three tubes of 

 slanted agar. If, after incubation, these tubes present normal 

 cultures of the dysentery bacillus the result of the test is negative. 

 That is, the original material did not contain an active bacterio- 

 phage for B. dysenteriae Shiga. The presence of the bacteriophage 

 in active form is indicated by an abnormal appearance of the 

 growth as it develops on the agar. In accordance with the num- 

 ber of bacteriophagous ultramicrobes present the aspect of the 

 culture will vary. The layer of bacillary growth may show one, 

 or several, circular areas where the surface of the agar appears 

 devoid of growth. Or, the culture may appear broken up, or 

 corroded, as a result of the confluence of the areas. Indeed, 

 there may be only fragments of culture or even isolated colonies 

 remaining. When the number of ultramicrobes is still greater 

 the slant may be free of any evidence of bacterial growth. 



As will be shown, each strain of bacteriophage is endowed with 

 an individual degree of virulence, the word " virulence' ' to be 

 taken in its true meaning, that is, " ability to multiply at the 

 expense of the parasitized being." Certain races of the bac- 

 teriophage multiply rapidly, others increase but slowly. The 

 first possess a high degree of virulence toward the bacterium 

 provided for their development; the second possess but a feeble 

 virulence. We will elsewhere return to this subject of the viru- 

 lence of the bacteriophage. It is mentioned here simply to ex- 

 plain the reason why strains of the bacteriophage show varia- 

 bility in growth when isolation is attempted. The diameter of 

 the clear areas, varying with the individual strain of bacterio- 

 phage from a fraction of a millimeter (the bacterial growth appears 

 as though sprinkled with pin point areas) up to 4jtoJ> mm., gives 

 a measure of virulence; the larger the area the higheTthe viru- 

 lence. We shall see that whatever the virulence of a particular 



