ANALOGY BETWEEN REACTIONS 551 



Friedmann have shown that suspensions of mastic may be ''protected" 

 against the precipitating action of ferric hydroxid by the addition of a 

 small amount of organic colloid, such as serum, leech extract, or extract 

 of typhoid bacilli, regardless of whether this colloid is charged posi- 

 tively or negatively or is neutral. The aforenamed observers believe 

 that normal bacteria may be surrounded by a similar protective envelop 

 that prevents the agglutinating action of substances of opposite sign. 

 The action of agglutinin, therefore, would be to remove this layer, so 

 that the ions of opposite electric charge can unite with the bacteria and 

 bring about their agglutination. This may be an explanation of the 

 role of salts in the phenomenon of agglutination, the agglutinins remov- 

 ing the protecting envelops and the salt furnishing the ions of opposite 

 charge that bring about agglutination. 



Owing to the fact that a discrepancy arises here for the reason that 

 emulsions of red corpuscles are agglutinated by both positive and 

 negative colloids (ferric hydroxid and cuprum ferrocyanid), Girard, 

 Mangin and Henri have given the following explanation of agglutina- 

 tion: When a red corpuscle is suspended in a fluid, various salts, es- 

 pecially the sulphates of magnesium and calcium, are diffused, which 

 tends to facilitate the precipitation of negative and positive colloids, 

 so that each corpuscle comes to be surrounded by a layer of precipitated 

 colloid material. This zone of precipitated colloids of either negative 

 or positive charge determines agglutination in the presence of a colloid 

 solution of opposite charge, such as agglutinin or inorganic colloids 

 (silicic acid, etc.). 



3. Hemolysins. Reference has been made elsewhere to the original 

 observations of Bordet, showing that red corpuscles may absorb much 

 more hemolytic antibody than is necessary to bring about their lysis, 

 and that this absorption is analogous to colloidal absorption. 



Inorganic colloidal solutions, such as that of silicic acid, may produce 

 hemolysis of red blood-corpuscles, e. g., those of the rabbit. Its action 

 is manifested in extremely small doses. It is rendered inert by heat, 

 and gradually deteriorates at room temperature. Furthermore, this 

 inorganic colloid possesses some of the properties of a serum hemolysin; 

 thus mice red corpuscles that have been agglutinated by colloidal silicic 

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

 that has been heated to 60 C. (inactivated). An excess of silicic acid 

 tends to prevent hemolysis, which is another example of the action of an 

 excess of one colloidal solution upon another of opposite sign. 



Probably saponin hemolysis and the influence of fatty substances, 



