FERMENTS, ENZYMES, TOXINS AND PTOMAINS 61 



plant cells in the infusion, whose chlorophyl sets free oxygen 

 in the light, are surrounded by large numbers of bacteria. 

 The positive chemotactic affinity between oxygen and 

 bacteria was employed by Engelmann as a basis for the 

 demonstration of small quantities of oxygen in studying the 

 influence of various kinds of light upon the assimilation of 

 green plant-cell. Pfeffer showed that when a neutral fluid 

 (a drop of water) containing motile bacteria is brought in 

 contact with a weak solution of either peptone, sodium 

 chloride, or dextrin, the bacteria are at once attracted 

 toward the solution; this reaction is designated "positive 

 chemotaxis." On the other hand, if brought in contact with 

 an acid, an alkaline, or an alcoholic solution, the bacteria 

 are repelled or driven from the point at which the two fluids 

 are diffusing; that is, they exhibit "negative chemotactic" 

 affinities. The significance of these reactions is not under- 

 stood, but it has been aptly suggested that they may be 

 fundamentally analogous to the specific positive and negative 

 affinities exhibited by the ions resulting from dissociation 

 of electrolytes, and that they may "have their explanation 

 in the forces of ionic attraction and repulsion." 1 In this 

 connection it is important to note that the wandering 

 cells of the animal body, the leukocytes, exhibit also these 

 chemotactic phenomena; and it is- especially necessary to 

 a complete comprehension of the process of suppuration to 

 bear in mind that among the substances which have the 

 greatest attraction for these wandering cells, are the products 

 of growth of certain bacteria in some cases, and the protein 

 constituents of the bacteria themselves in others. 



1 Read Sewall on Some Relations of Osmosis and Ionic Action in Clinical 

 Medicine, International Clinics, vol. xi, Eleventh Series. 



