218 4 



In the same way they suppose that there exist in the bacteria a group that 

 is but little resistant, the agglutinophore, and a second more stable group with 

 which the agglutinine unites, i. e. Ehrlich's haptophore group. 



Our own researches have been made with the special object of ascertaining the 

 precise nature of the changes produced both in the agglutinating immune-serum 

 and in the bacteria by the action of various physical and chemical agents upon 

 them ; and of clearing up a few of the questions to which the numerous investigations 

 into the nature of bacterial agglutination published during the last few years have 

 given rise. 



A. Experimental Methods. 



Most of the following experiments were made with growths from a stock cul- 

 ture of Bacillus coli communis on the one hand, and with the agglutinating immune- 

 serum derived from goats or rabbits after they had been immunised by injections 

 of this race of bacteria on the other; this is the serum and these are the bacteria 

 employed throughout the following experiments wherever no special statement is 

 made to the contrary effect. Additional experiments were made in certain cases 

 with B. typhosus and the corresponding typhosus-agglutinating immune-serum. 



Following earlier observers we have usually employed an agar- or bouillon- 

 culture 24 hours old: the age is specially mentioned where this is not the case. In 

 the great majority of our experiments agar-cultures were employed, for two reasons; 

 firstly, because we wished our experiments to correspond as closely as possible with 

 those of the various writers already mentioned; and, secondly, because emulsions 

 of the bacteria grown upon agar are free from the presence of the numerous un- 

 known chemical substances contained in the bouillon-cultures, and are therefore 

 more likely to give precise and uniform lesults. 



On the one hand, the use of bouillon-cultures is not without its advantages; 

 such cultures are easily prepared, and expose the bacteria to the action of the agglut- 

 inine with the least possible disturbance of the natural conditions under which 

 they have been grown. 



On the other hand, there are two great objections to the use of bouillon-cul- 

 tures; one is the presence of many unknown substances in them, as has been already 

 stated; the other is the fact that one has no exact control over the number (or con- 

 centration) of the bacteria in such cultures, for different 24-hour growths may show- 

 considerable variations in this respect. Finally the very general tendency of bouillon- 

 cultures of \i. coli communis to spontaneous agglutination must be mentioned, a 

 phenomenon recorded by a large number of experimenters, and one upon which 

 too much stress has often been laid. 



