242 



SCIENCE 



[N. S. Vol. XXIX. No. 737 



lishment of curative serum therapy by 

 Behring when he demonstrated that anti- 

 toxic serum protects healthy animals 

 against fatal doses of the corresponding 

 toxin and may even cure the already sick, 

 served to turn to the common good this in- 

 nate faculty of the animal body to develop 

 in so marvelous a manner its own resources. 



Let it be noted once more that serum 

 treatment, which has robbed diphtheria of 

 its former terrors and the benefits of which 

 are being extended to other diseases, is the 

 direct outcome of scientific animal experi- 

 mentation, and that without such experi- 

 mentation it would not have been dis- 

 covered and could not be maintained and 

 extended. 



The new methods and principles de- 

 veloped by the study of the animal reac- 

 tions to infection did not long remain the 

 exclusive property of the workshop of the 

 bacteriologist. Ehrlich 's side-chain theory 

 of toxic and antitoxic action proved most 

 heuristic, leading directly to fruitful in- 

 vestigation of other fields, and to-day 

 biology, clinical and legal medicine, and 

 physiological chemistry are using im- 

 munological methods to solve important 

 problems. 



According as stress was placed on the 

 part of phagocytosis, on the one hand, and 

 on the role of antibodies, antimicrobic as 

 well as antitoxic, on the other hand, in- 

 vestigators until but recently were largely 

 partisans of either the phagocytic or the 

 humoral theory of healing and immunity. 

 But the sharp antagonism between the ad- 

 herents of these theories has subsided, 

 because it has been made clear that neither 

 mode of action is accomplished without 

 the cooperation of cells and fluids. This 

 is particularly true and easy of demonstra- 

 tion in the case of phagocytosis. Metehni- 

 koff, the genial founder of the phagocytic 

 theory, by broad comparative studies es- 

 tablished the general occurrence and the 



significance in health and disease of phago- 

 cytosis in the higher as well as in the 

 lower animals, and Denys and others have 

 shown that the fluids of the blood play an 

 essential part in the phagocytic process by 

 so acting on microbes and other elements 

 that they are made susceptible of phago- 

 cytic action. This property of the blood- 

 fluid is now ascribed to definite sub- 

 stances, the opsonins of Wright and Doug- 

 las, and the tropins of Neuf eld, both in all 

 probability the same substances, and des- 

 tined, I believe, to bear the name of opson- 

 ins, at least in the English language. 

 While our acquaintance with the opsonins 

 dates back only four or five years, they 

 have been the subject of many researches, 

 and much has been written about them, 

 and it is to some more or less final results 

 and certain general bearings of this work, 

 fruit of the phagocytic theory as modified 

 and perfected by the opsonic theory, that 

 I wish to direct your attention. 



It is generally accepted that phagocy- 

 tosis of many bacteria— and also of red 

 blood corpuscles, which are highly service- 

 able objects for the study of certain prob- 

 lems—is dependent upon substances — 

 opsonins — which become attached to the 

 bacterial cells or corpuscles, as the case 

 may be, and so alter them that they are 

 readily taken up by the leukocytes. The 

 chief reasons for this conclusion are that 

 leukocytes, carefully freed by repeated 

 washing in salt solution, from the fluids in 

 which they naturally exist, have but very 

 little or no phagocytic power with respect 

 to certain bacteria or corpuscles suspended 

 in salt solution, while the same bacteria or 

 corpuscles, after having been treated with 

 suitable opsonic serum and then freed 

 from the serum, are taken up by serum- 

 free leukocytes. A few bacteria, however, 

 e. g., influenza bacilli, are readily phago- 

 eytable without the presence of opsonic 

 serum. 



