OPSONINS. 



177 



phagocytosis will not take place, or will do so imperfectly. The belief of 

 some authors that "spontaneous phagocytosis" without serum was alto- 

 gether impossible, was disproved, especially by Lohlein. The manner in 

 which the serum acts, whether it stimulates the digestive activity of the 

 leucocytes or whether it so changes the bacteria that they can more readily 

 be taken up by the phagocytes, has been settled in favor of the latter view 

 through researches, especially of Wright and his followers as well as by 

 Neufeld. The substances within the serum which thus modify the bacteria 

 have been designated by Wright as "opsonins." ("opsono" = I prepare 

 food for). 



Opsonins are demonstrated by mixing bacteria, serum and washed 

 leucocytes, allowing this mixture to remain in the incubator for a short time, 

 and then staining smear preparations. Wright then counts a certain num- 

 ber of leucocytes and the number of bacteria found within these leucocytes. 

 The relation between this number of ingested bacteria and the 

 The Opsonic counted number of phagocytes is designated as the phagocytic 

 Index. count. Wright compared the phagocytic counts of infected 

 individuals with those of normal persons and found that those of 

 the former were much lower. The relation existant between the two he expressed 

 in the form of a fraction and that is known as the opsonic index. Thus a smear 

 made from a mixture of equal parts of an emulsion of staphylococci, leuco- 

 cytes and the patient's serum showed for example 75 cocci to 100 leucocytes; 

 while one made from a mixture of equal parts of the same bacterial emulsion, 

 leucocytes, but a normal individual's serum demonstrated 150 bacteria to 100 

 leucocytes. The opsonic index of the patient's serum would therefore be 

 one-half (0.5). 



According to Wright, the opsonic index expresses the animal's resistance 

 against infection. He believes that a low opsonic index for a given bacter- 

 ium indicates a susceptibility on the part of the individual for that particular 

 infective agent. Furthermore, the opsonic index he claims can be used as an 

 aid in the diagnosis of infectious diseases, inasmuch as opsonins are specific. 

 Thus the opsonic index in a tuberculous individual is low only for the tuber- 

 cle bacillus and not for other bacteria. 



When an animal is immunized, its opsonic index toward the respective 

 bacterium is considerably increased. The question has been asked whether 

 the immune opsonins formed during this process are identical with the nor- 

 mal opsonins. Wright and a number of the more recent authorities believe 

 that they are different. Neufeld, who discovered these immune opsonins 

 independently of Wright, named them Bacteriotropins, and pointed out 

 that while the normal opsonins are destroyed when heated to 56, the bacterio- 

 tropins remain unharmed. As yet the exact nature of the immune as well as 

 of the normal opsonins has not been clearly defined. It is still a matter for 

 investigation whether in the case of opsonins one is dealing with entirely new 



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