4 STUDIES l.\ [MMUNITY. 



These experiments show us, moreover, that a vibrio that has 

 undergone two passages is only slightly less attracting than one 

 that has undergone a single passage. 



Let us now consider whether the toxicity of the bacterial secre- 

 tions has changed in a manner similar to that of the chemiotactic 

 property. 



Experiment 2. A healthy guinea-pig, weighing G20 grams, was 

 given an inoculation of 6 c.c. of a very virulent, modified, sterilized 

 culture. Although this amount was rather small, it killed the 

 animal in 60 hours. At autopsy no lesions other than intestinal 

 congestion were noted. 



Another guinea-pig, weighing 450 grams, received 5.5 c.c. of the 

 ordinary vibrio Metchnikovi, which in proportion to the weight of 

 the animal was slightly more than was given the preceding animal. 

 This animal showed no effect, however, and remained in good condi- 

 tion. 



It is to be noted that an increase of toxicity here accompanies a 

 lowering in positive chemiotactic power. 



To what is this weakness in attraction due? Are w r e to regard it 

 simply as a quantitative decrease in the attracting substance that 

 the normal vibrio produces so abundantly? Or is there formed, on 

 the contrary, a repelling substance of which little or none is formed 

 by the original vibrio? An attempt to reply to these questions 

 follows. 



Experiment 3. We placed in the peritoneal cavity of a normal 

 guinea-pig capillary tubes containing the following vibrios, pre- 

 pared on the same culture media as in experiment 1 : 



(a) Normal sterilized culture of vibrio Metchnikovi. (b) Steril- 

 ized culture of the vibrio Metchnikovi from the exudate withdrawn 

 from the second immunized guinea-pig. (c) A mixture of equal 

 parts of the two first fluids, (d) A mixture of equal parts of fluid 

 "b" and sterile culture medium, identical with that on which 

 the organisms had been grown. 



These tubes were left in the animal body for 8 hours. On exami- 

 nation the columns of leucocytes in tubes containing liquids "a," 

 "c," and "d" were seen to be equal. In the "b" tubes the length 

 of the column of leucocytes was less than half this. 



A consideration of tube " d" shows us that dilution with an inert 



