35 2 SEQUENCE OF EVENTS IN LOCAL LESIONS 



too, that they may have become so altered in virtue of having 

 once been stimulated to produce antibodies that they can do so 

 more quickly and easily than normal cells. Thus Cole has shown 

 that an animal which has once been inoculated e.g., with typhoid 

 bacilli will produce on a second injection a much greater output 

 of antibodies than will a normal animal, and that this increased 

 defensive reaction persists for months, long after the animal has 

 apparently become normal. This observation is probably of the 

 highest importance, both as regards general and local acquired 

 immunity. 



Thus in the case of a local lesion we may distinguish two 

 stages : ( i ) That in which the natural resources of the body alone 

 come into action, and in which the main mechanism for com- 

 bating the bacteria is phagocytosis, the main cell the polynuclear 

 leucocytes, and the main defensive substance the thermolabile 

 opsonin. In this stage there is in general a decline of the local 

 immunity due to the action of toxins on the tissues, and the only 

 rise of the general immunity, if present at all, is due to an increase 

 of this opsonin. (2) The second stage is that of the antibodies. 

 The factors taking part in the first stage persist, but there is a 

 new defensive cell, the lymphocyte, and new defensive substances, 

 the antibodies. Here the immunity, both local and general, tends 

 to be raised. We may also distinguish a third stage, in which the 

 polynuclears have retired and the lymphocytes remain a stage in 

 which the natural immunity of the part is reinforced by the actual 

 or potential opsonins due to the lymphoid cells, and in which 

 these are better equipped (in virtue of their previous training) to 

 produce a large amount of antibody in response to a slight 

 stimulus. 



Lastly, we must study briefly the defensive reactions of the 

 peritoneum, a region which has been subjected to a full investiga- 

 tion and which resembles the tissues in some points and the blood 

 in others. In all probability the process of absorption from the 

 other serous sacs is, in general, similar. We have already glanced 

 at the subject, and in what follows much use has been made of 

 the admirable researches of Buxton and Torrey. The case of an 

 intraperitoneal injection of a pathogenic organism of moderate 

 virulence into an animal possessed of a certain amount of natural 

 immunity will be considered e.g., of a laboratory culture of 

 B. typhosus into the peritoneal cavity of the rabbit. 



Under these circumstances, one or other of two trains of events 



