326 COLLOIDS AND HAEMOLYSIS 



extract of typhoid bacilli, and they think that normal bacteria 

 may be compared with these particles surrounded by a defensive 

 envelope which prevents the flocculating action of substances of 

 opposite sign. The action of agglutinin they believe to consist in 

 the removal of this layer, so that then the ions of opposite sign 

 can unite with the bacteria and bring about their agglutination. 

 This explanation would explain clearly the role of salts in agglu- 

 tination, and is supported by Kirstein's observation that typhoid 

 bacilli cultivated in medium free from albuminoid material is 

 clumped by salt without the addition of serum. The theory, how- 

 ever, appears at present not to account for the facts already cited 

 with regard to the transport of normal and charged bacteria in an 

 electric current. 



Some remarkable analogies have been brought forward by 

 Landsteiner and Jagic between the process of haemolysis by 

 simple colloids and by specific antibodies. Thus a solution of 

 colloidal silicic acid acts in a manner closely recalling a specific 

 haemolysin. It clumps and dissolves the red corpuscles of rabbits, 

 and agglutinates their spermatozoa, but has no action on typhoid 

 bacilli ; it thus shows signs of selective action, though not of true 

 specificity. Its action is manifested in extremely small doses ; it 

 is rendered inert by heat, and gradually falls off even at the room 

 temperature. Further, phenomena are observable which strongly 

 recall the action of complements and of lecithin in reactivating 

 heated serum or in dissolving sensitized corpuscles, since red 

 corpuscles which have been agglutinated by colloidal silicic acid 

 are dissolved by traces of lecithin or of fresh serum, but not by 

 serum which has been heated to 60 C. ; but if the silicic acid 

 is present in excess, no haemolysis occurs. 



A difficulty arises from the fact that emulsions of red corpuscles 

 are agglutinated by both positive and negative colloids (ferric 

 hydroxide, ferrocyanide of copper). Girard-Mangin and Henri 

 have given an explanation of this, which is briefly as follows : 

 When a red corpuscle is suspended diffusion of salts, especially 

 of sulphates of calcium and magnesium, takes place from their 

 surface, and these facilitate the precipitation of positive and 

 negative colloids respectively, so that the corpuscles come to be 

 surrounded by a layer of precipitated colloid material. It is this 

 zone of precipitated material which actually determines the agglu- 

 tination of the corpuscles. Thus these authors consider three 

 substances as taking part in the process : (a) the corpuscles ; 



