ADAPTIVE CHANGES OF BACTERIAL CULTURES. 5 



fluid increases the attracting power of the "modified" vibrio Metch- 

 nikovi and renders it quite as energetic as the normal organism. 



We may then put aside the hypothesis that the modified vibrio 

 has lost a part of its attracting properties owing to a smaller amount 

 of positive chemiotactic substance. There is evidently a negative 

 chemiotactic influence which lessens to a considerable degree the 

 effect of the attractive substances. Experiment shows us that 

 dilution weakens the activity of the first more than that of the 

 second. 



There is nothing to prove that these substances, acting in an 

 opposite manner on white corpuscles, are distinct. It may be that 

 there are not two different chemical substances, but that one and 

 the same substance may attract leucocytes when diluted and repel 

 them when concentrated. This last hypothesis is far from difficult 

 to accept: we know, indeed, the profound influence which the con- 

 centration of various substances has on their power to affect sus- 

 ceptible cells. This is not a supposition, however, that we have been 

 able to prove. 



Whatever the substance may be to which the repelling action is 

 due, it is present and acts energetically in the modified vibrio, but 

 it is also manifest to a less degree in the ordinary organism. As a 

 matter of fact, the attracting power of the secretions of this latter 

 organism increases with dilution, as demonstrated by a capillary 

 tube experiment. 



The vibrio that has been grown in an immunized guinea-pig does 

 not long retain its intense repelling property when grown on arti- 

 ficial media. 



Experiment 4. A comparison was made as regards chemio- 

 taxis, by the same method of capillary tubes, between the vibrio 

 Metchnikovi cultivated for a long time on agar tubes and a vibrio 

 marked "very virulent" that had been transplanted every four 

 days for nearly half a month in veal bouillon containing 1 per cent 

 peptone. The leucocytes filled equal lengths of the tubes of each 

 strain. 



We have seen that residence in the body of a vaccinated animal 

 lends certain modifications to the vibrio Metchnikovi; it becomes 

 more toxic and less attracting for leucocytes. Let us now consider 

 how these modifications are produced. 



