220 Dr. A. E. Wright and Staff-Surgeon S. T. Eeid. [Oct. 21, 



persons who have responded to tubercular infection, or as the case may be to 

 the inoculation of a tubercle vaccine, is an opsonin. We may, pending the 

 discussion in the next section of its identity and non-identity with the opsonin 

 of the unheated normal serum, speak of this opsonin in a provisional manner 



aa the opsonin found in the heated immune serum. 



Question as to whether the Opsonin found in Heated Immune Serum is or is not 

 Identical with that found in the Unheated Normal Serum. 



Leishman, who has spoken of the incitor element in the heated immune 

 serum as a stimulin, in common with Neufeld, working in conjunction with 

 Eimpau, and Dean, who have shown that this incitor element functions as an 

 opsonin, have laid emphasis on the thermostability of the incitor element. 

 Both Leishman and Neufeld urge that the character thermostability differen- 

 tiates the incitor elements they have in view from the thermolabile opsonins 

 described by one of us in conjunction with Douglas. Neufeld goes further, 

 and contends that the particular opsonins which have been described by 

 him as thermostable alone possess any significance in connection with tbe 

 protection of the organism against bacterial disease. In support of this 

 contention Neufeld adverts to the fact that man, although he is, according to 

 experiments recorded by one of us in conjunction with Douglas, the possessor 

 of thermolabile opsonins against the plague bacillus, is none the less not 

 protected against this micro-organism. 



Before investigating the question of fact as to the identity or non-identity 

 of the opsonins of the normal and immune organism, which are discriminated 

 from each other by Neufeld, we may be allowed to comment on the stand- 

 point which he takes up. We submit that he proceeds upon an entirely 

 erroneous conception when he assumes that the non-immunised human 

 organism does not offer a resistance to such bacterial infections as plague. 

 We submit, further, that it is erroneous to conceive of the normal organism 

 as differing from the immunised organism in a qualitative manner. Bather, 

 does not the theory of Ehrlich brilliantly teach that in immunisation we are 

 never building upwards from a level of absolute non-resistance, but always 

 building upon a foundation which is already laid — calling into existence in 

 increased quantity and conveying into the blood only such chemical agents 

 as exist already preformed in the body ? 



Beverting from this digression, we may address ourselves to the investiga- 

 tion of the facts, and may inquire whether they plead against or in favour of 

 the identity of the opsonins which are found in the unheated normal blood 

 with the opsonins which are found in the heated immune blood. 



In the investigation of the facts we have built upon the following 

 postulates : — 



