.8io THE FUNCTIONAL ROLE OF AGGLUTININS 



fection of the dog, an animal relatively immune to the pneumococcus, in which both 

 typical intravascular agglutination and chain formation occurred, the latter in the 

 cerebrospinal fluid. 



Another way in which agglutinins may play a part in defense, over and above that 

 of agglutinating the bacteria, is by the physico-chemical alterations produced by the 

 agglutinins, which are believed to act by digesting or otherwise altering the protective 

 colloidal envelope which interferes with chemical reactions between the bacteria and 

 the surrounding fluids. When this protective layer is destroyed by the agglutinins 

 the permeability of the bacteria for various ions, including bactericidal substances, is 

 increased. It is probable, therefore, that the agglutinins play a considerable part in 

 this way in aiding other serum constituents in the actual destruction of micro-organ- 

 isms. 



It must be concluded that the mechanism of removal of bacteria from the body 

 of an animal host is a complex one. Most of the evidence seems to show that the 

 humoral part of the process consists in an increased adhesiveness of the micro-organ- 

 isms by which they agglutinate into clumps of widely varying sizes, and are then either 

 filtered out by the visceral organs or stick to leukocytes, to endothelial cells, or 

 to platelets. In addition, there is active phagocytosis by polymorphonuclear and 

 mononuclear cells of the blood and the cells lining the sinuses of the liver, lungs, and 

 spleen. In the skeletal tissue spaces agglutinins probably do not play as great a part 

 as in the circulating blood. In these situations direct bactericidal action and phag- 

 ocytosis are probably very important factors. 



SUMMARY 



1. Certain clinical observations have shown a parallelism between the power of a 

 serum to cause agglutination of bacteria outside the body and its power to bring 

 about intra vitam agglutination and recovery from infection. 



2. Experimentally agglutination can be demonstrated in vivo; the power of the 

 blood to cause agglutination determines largely whether after their direct introduction 

 in an experimental way bacteria are to be removed from the circulation. 



3. The power of the blood to produce agglutination in vivo may not be demon- 

 strable in vitro. Agglutination occurs much more readily and promptly in the animal 

 body than in the test tube. 



4. The degree of agglutination and opsonization of bacteria within the body is in 

 general inversely parallel to the virulence of the micro-organisms for the host. 



5. Bacteria which are not agglutinated in the circulating blood of the normal ani- 

 mal may be agglutinated by the intravenous injection of a specific immune serum. 

 Such serum is many times more active in vivo than in vitro. 



6. Agglutination in the infected animal may have a definite protective function 

 through a preliminary concentration of bacteria in the capillaries of the visceral organs 

 whereby phagocytosis is facilitated. 



7. Agglutinins, opsonins, and phagocytosis are very closely related, and exert an 

 important role in resistance to, and recovery from, infection. 



