INTRODUCTION 15 



Twort states that when a drop of a filtrate containing his active 

 principle is spread upon the surface of an agar slant and this tube is 

 next inoculated with a normal culture of the staphylococcus, a normal 

 growth of the staphylococcus commences to develop. Then it under- 

 goes a vitreous transformation, the change having its inception at 

 certain points, to later spread throughout the whole extent of the bac- 

 terial layer. If the principle is but slightly diluted the glassy trans- 

 formation occurs at the same time that the growth takes place. 



In the phenomenon of bacteriophagy, if one spreads upon an agar 

 slant a drop of filtrate containing a little of the bacteriophage principle, 

 and if one then inoculates the surface by spreading over it a suspension 

 of the staphylococcus, one obtains a culture for the most part absolutely 

 normal in appearance, but here and there small islands, circular plaques, 

 are found, where the agar is bare without any trace of growth in any 

 form whatever. These plaques undergo no change, even after several 

 days. They never invade the surrounding culture, nor are they ever 

 covered by the bacterial growth. All about these plaques, the cul- 

 ture, retaining its normal appearance, is formed of cocci preserv- 

 ing their normal microscopic form. When one spreads upon the 

 agar a filtrate containing a large quantity of the bacteriophage, and 

 when one next seeds it with a normal culture of the staphylococcus, 

 the agar surface, after incubation, remains naked, free of all evidences 

 of bacterial growth or of anything visible. 



If, says Twort, there remain in an infected tube some small regions 

 where the culture is normal, these micrococci develop and invade the 

 areas covered by the transparent material. 



I have already stated that in bacteriophagy the plaques, isolated or 

 confluent, where the agar is bare, remain unchanged and are not re- 

 covered by the normal surrounding culture, and this is true even if 

 there be but a single plaque upon the entire surface of a culture, and 

 even if this plaque is very small, having a diameter of but a fraction of 

 a milHmeter. 



Twort states that if a normal culture of susceptible staphylococci is 

 touched with a trace of the "transparent material" derived from a 

 vitreous colony, the culture at the touched point becomes transparent, 

 and the transformation next extends over the entire culture, the 

 micrococci being replaced by granules. 



If one touches an agar culture of staphylococci, young or old, in 

 one or in many places, with a fluid containing the bacteriophage, or 

 even if one touches a normal culture with a platinum wire previously 



