226 LECTURES ON IMMUNITY 



not pass into ea to give the compound eab which gives 

 bacteriolysis. It is mere chance whether the affinity of b 

 for a is greater than for ea, as in this case, or less, in which 

 case haemolysis would occur." This extremely artificial 

 explanation seems to me quite erroneous. For if we have 

 the compounds ea and ab and the compound eab may be 

 formed, its formation depends wholly upon whether e has 

 a greater affinity for ab than for a. 1 If not, then eab is 

 not formed, even if a is not present in excess. Therefore, 

 if Ehrlich's idea were right, no bacteriolysis should occur 

 in Neisser and Wechsberg's experiments, and no haemo- 

 lysis in the experiments cited above. 



The probable cause is the following. If a is large, it is 

 not totally absorbed by the cells, but a fraction of it 

 remains in the surrounding fluid, and this part increases 

 rapidly with increasing a (cf. p. 150). a forms a com- 

 pound (ab) with b as well outside the cells as within them. 

 This compound is partially dissociated, so that its quantity 

 increases and the quantity of free alexin b decreases with 

 increase of a in the liquid. At very high excess of a, b 

 may become practically wholly bound. This seems to 

 have been the case in Neisser and Wechsberg's experi- 

 ment (the errors of observation are too great to give a 

 final decision). The membranes of the cells are (cf. p. 22 r) 

 practically impermeable to the lysin (ab\ and only the 

 lysin formed from a and b within the cells is active. As 

 there is now very little (or practically no) free b in the 



1 It is assumed that the amount of a exceeds the quantity which is neces- 

 sary to bind (produce lysis with) the quantities e and b. This necessary 

 quantity of a is rather unimportant, about 2 in my experiments cited above, 

 and even in Neisser and Wechsberg's experiments this condition has proba- 

 bly been fulfilled long before a gave a maximum. 



