270 president's address — section l. 



the contact and adhesion of the foreign particle or cell with the 

 phagocyte, and then its ingestion. In the formei- stage the phago- 

 cyte is probably quite passive, the particle having been subjected 

 by reason of its adsorption of opsonins to a physico-chemical change 

 which facilitates adhesion, whilst the latter stage is due to the 

 amoeboid mobility of the leucocyte. Ledingham (1906) has 

 shown that in the presence of op.sonins bacteria have a tendency 

 to adhere to leucocytes even at temperatures too low for amoeboid 

 action to occur. 



One last observation on the methods of phagocytosis is that 

 named by Bordet the jihagoci/tarjj crhis. If a rabbit is injected 

 intraperitoneally with bouillon, and at the same time receives a 

 dose of autistrepLC'Coccic serum, it can then receive on the following 

 day a fairly large dose of virulent streptococcus culture with the 

 following results. Thanks to the immune serum injected the 

 bacteria are prevented from invading the body genei"ally ; very 

 numerous polymorphs are present in the exudate ; but the strepto- 

 cocci even aiter several hours are still free, have surrounded 

 themselves with a kind of aureole (capsule) and the exudate is 

 almost purulent. Then begin to appear large mononuclear cells 

 (macrophages) and almost suddenly extensive phagocytosis of strep- 

 tococci by these large cells occurs. The polymorphonuclear cells 

 are in the main inactive, many are dead, but just before phago- 

 cytosis occurs the streptococci may also be seen to be abnormal, 

 staining feebly, smaller in size, whilst the aureole is indistinct. 

 This is the moment when phagocytosis commences. Bordet's ex- 

 planation is very simple. The protective measures have prevented 

 the cocci from becoming septicaemic, the macrophages derived from 

 endothelial cells and lymph glands have begun to mobilize, and 

 the breakdown products (ferments) from the dead polymorphonu- 

 clears have commenced an extracellular digestion of the bacteria. 

 The joint action of opsonins and macrophages completes the scheme 

 of defence, and if the dose of streptococci has not been toO' large 

 the animal reccvers. 



We may conclude this view of the action of phagocytes by 

 saying that the opsonic hypothesis of Wright has gone far to 

 reconcile the cellular and humoral theories by bridging the gap 

 and demonstrating their essential co-operation in the whole plan 

 of immunity mechanism. 



But now to consider more closely the role of the serum in the 

 production of immunity. 



Bole of the Sei'iim : Anfif/enx and Anfihodies. 



Any review of the development of the science of immunity 

 must bring out in strong light the ever-recurring tendency of 

 workers in this field to generalize from very limited observations, 

 to stumble across an important discovery and at once toi enunciate 



