212 Dr. A. E. Wright and Staff-Surgeon S. T. Keid. [Oct. 21, 



Savtschenko* obtained in experiments conducted in vitro with the heated 

 sera of animals which had been subjected to injections of red blood corpuscles, 

 phagocytosis of these formed elements. 



Neufeld and Rimpau,\ working with heated sera derived from animals which 

 had been immunised against streptococcus and pneumococcus, and conducting 

 their experiments in vitro, have described these immune sera as possessing a 

 power of inciting phagocytosis. This power was, be it remarked, not 

 numerically measured. 



Leishman,% employing the numerical method for the measurement of 

 phagocytosis which was devised by him with the modifications introduced 

 by one of us in conjunction with Douglas, ascertained that the sera derived 

 from Malta fever convalescents, or as the case may be from men who had 

 undergone anti-typhoid inoculation, retain, after heating, elements which 

 promote phagocytosis. 



Dean, working with the same methods, without however conforming to the 

 easily realised conditions§ which are essential to the accuracy of the 

 enumeration, has described incitor elements in the heated serum derived 

 from animals which had been immunised against staphylococcus. 



Lastly, Douglas, employing again the same methods, has obtained evidence of 

 the presence of an incitor element in the heated serum derived from himself 

 and others after inoculation with a sterilised culture of the plague bacillus. 



Views of the Observers above mentioned on the Nature of the Incitor Element 

 contained in the Heated Serum. 



Influenced by the theoretical conception that the increased resistance to 

 bacterial invasion which is obtained by bacterial inoculation is in every case 

 referable to a modification of the phagocytes,|| Metchnikoff originally spoke 

 of the incitor element as a stimulin. 



* ' Annales de l'lnstitut Pasteur,' 1902. 



t Neufeld and Eimpau's paper was published in the ' Deutsche Med. Wochenschrift ' in 

 September, 1904, 12 months after the first description of the opsonins in these 

 ' Proceedings.' 



X ' Path. Soc. Trans.,' 1905, vol. 56. 



§ " I should not feel disposed," remarks this author (' Koy. Soc. Proc.,' Series B, vol. 76, 

 p. 511), " to place quite the same reliance as Wright and Douglas on the numerical 

 accuracy of the results which can be derived from their method. Where the leucocytes 

 are very full, i.e., where the counts are high — it is impossible to differentiate results by 

 the method of enumeration." In spite of the perfectly self-evident experimental limita- 

 tion of our method, which Dean here recognises, this worker employs in practically all 

 his published experiments bacterial suspensions which give him an average phagocytic 

 count often of 50 and more bacteria in the leucocyte. Such a count is altogether 

 incompatible with accurate quantitative work. 



|| The correctness of the view that artificial immunity depends upon a modification of 



