344 SEQUENCE OF EVENTS IN GENERAL INFECTIONS 



susceptible animal somewhat as follows : The bacteria form a 

 toxin which attracts the leucocytes from the bone-marrow into 

 the blood, and which also stimulates their production in larger 

 numbers. It also attracts the leucocytes into the neighbourhood 

 of the bacteria, and this process is more marked in regions, such 

 as the spleen and bone-marrow, in which the flow is slow. As a 

 result some leucocytes are stimulated to produce complement, or, 

 on the other theory, are killed, and their complement set free. In 

 either case the bacteria are prepared for phagocytosis. This 

 process may now take place, the bacteria be destroyed, and the 

 infection come to an end. This is a type of a mild infection. 



Or it may happen that the toxin is so powerful that the leuco- 

 cytes are repelled, or, if attracted, immediately killed. If this 

 occurs the sole resource of the patient is the bacteriolytic property 

 of the blood, which will then come into action provided, of course, 

 that the bacterium is one to which amboceptor occurs in the normal 

 blood because alexin is set free in the solution of the leucocytes. 

 Experiment, however, leads us to believe that this is a slower 

 and less important process than phagocytosis, and that if the latter 

 is in abeyance the outlook for the patient is bad in the extreme. 

 If both processes fail the infection must be rapidly fatal. 



In an infection in which the defensive and offensive mechanisms 

 are nicely balanced, and an illness of some duration and severity 

 occurs, the processes will be much more complex. The early 

 stages will occur as in a mild infection, and the bacteria will be 

 surrounded by the leucocytes, and perhaps even ingested. In this 

 case it may happen that after ingestion solution will take place, 

 and an endotoxin be set free which will kill the phagocyte, and 

 perhaps also those in the immediate neighbourhood, and in this 

 way some of the bacteria may be shielded from further phagocy- 

 tosis for a time. This and similar processes give the bacteria 

 time in which to undergo their defensive modifications, which they 

 do in virtue of the " survival of the fittest " i.e., those which are 

 best adapted to their environment in the host. Now it is clear 

 that in any culture of bacteria the different individuals have 

 marked differences with regard to their power of absorbing anti- 

 bodies. This is obvious when we consider that otherwise the 

 addition of gradually increasing amounts of an agglutinating 

 serum would cause no effect until a certain concentration was 

 reached, when all the bacteria would clump. As it is, those 

 organisms with the greatest affinity take up the agglutinin in 



