ON IMMUNITY TO BACTERIA 355 



this process ; instead, large numbers of bacilli make their way 

 into the circulation by a route not fully known. These rapidly 

 decrease in number, the diminution being quite noticeable within 

 half an hour, and in six hours or less the blood may be entirely 

 sterile. There is, further, a remarkable amount of deposition of 

 the bacilli in the organs, especially the liver, spleen, lung, and 

 bone-marrow ; and in these situations the numbers of organisms 

 decrease for about two or three hours, and then show a very 

 definite rise, which lasts for two or three hours more, and the 

 organisms may attain numbers approximating to those present in 

 these organs immediately after the injection. The numbers then 

 gradually decrease for the next two days or so. Here we may see 

 in a very clear manner an example of the mobilization of the 

 defensive forces discussed previously. The diminution which 

 takes place immediately after the access of the bacilli to the 

 organs is doubtless due to the bacteriolytic substances, either 

 present in the blood as such, or immediately available after 

 phagolysis or secretion of alexin. After a time these substances 

 are exhausted, and it is only after some hours that a fresh supply 

 is elaborated, and destruction of bacilli continues. Further, the 

 process that now takes place is mainly phagocytosis, whereas the 

 earlier defensive process was bacteriolysis. This sequence of 

 events is probably to be interpreted as follows : As soon as infec- 

 tion takes place the small amount of immune body naturally 

 present in the blood combines with the bacilli, and, since some 

 complement is present, bacteriolysis occurs. In this way all the 

 immune body is removed in combination with the bacilli, and all 

 the complement is also absorbed, since the conditions for the 

 Bordet-Gengou phenomenon are present, and complement not 

 actually required for solution of bacilli will be taken up, as well 

 as that which is actually used in the process. Hence all the 

 defensive substances are removed, and the bacilli can flourish 

 unchecked for a time. Soon, however, more complement is 

 produced. This has little or no power of producing bacteriolysis in 

 the absence of amboceptor, but it can, and does, act as opsonin, 

 and abundant phagocytosis occurs. In most diseases this stage 

 would be marked by leucocytosis, but in typhoid fever this does 

 not occur. But we shall shortly see that a polynuclear reaction 

 does take place in the peritoneum, if not in the other regions. 



In the series of researches we are discussing the development 

 of the last line of research the true antibodies was not studied. 



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