58 THE DEFENSIVE FORCES OF THE MACROORGANISM 



direction. This is really what one would expect, remembering that 

 the proteolytic enzymes of the cell can hardly exercise any germicidal 

 action, and that in many of the lower forms of animal life there is 

 direct evidence of a destruction of the captured living cell prepara- 

 tory to its digestion. Much work, however, remains to be done in 

 this direction. 



While leukocytes are capable of taking up certain bacteria in the 

 absence of blood serum spontaneous phagocytosis the majority of 

 those organisms which are pathogenic for man and the higher animals 

 become subject to phagocytic action to a notable degree, only after 

 they have been exposed to the action of fresh serum. This fact was 

 emphasized already by Denys and Leclef, who noted that phagocy- 

 tosis was greatly facilitated if the process was permitted to take place 

 in the presence of serum from an animal that had been immunized 

 against the corresponding organism. In contradistinction to Metsch- 

 nikoff, who referred this peculiar effect to the possible presence in 

 the serum of substances which exercised a stimulating action upon the 

 activity of the leukocytes (stimulins), Denys and Leclef suggested 

 that the effect of the serum might be directed against the bacteria in 

 the sense that the exo- and endotoxins of the latter were neutral- 

 ized and the organisms thus deprived of their most active defensive 

 weapon against the phagocytic activity of the leukocytes. 



Opsonins. Wright and Douglas then proved that these substances 

 which they could demonstrate in normal serum also, actually prepare 

 the bacteria for phagocytosis. This was shown by suspending 

 organisms for a while in fresh serum, washing them with normal salt 

 solution and then exposing them to the action of leukocytes, when 

 phagocytosis promptly occurred, while similar exposure of the leuko- 

 cytes to serum and subsequent washing gave rise to negative results. 

 Wright and Douglas hence termed the substances in question opso- 

 nins (from the Latin verb opsonare, to cater to, to prepare pabulum 

 for), and expressed the opinion that the opsonins of normal serum and 

 immune serum are identical. 



Bacteriotropins. This, however, is denied by others, such as 

 Neufeld and Rimpau, who confirmed the findings of Denys and his 

 pupils on the presence of pro-phagocytic substances in immune serum 

 and named these bodies bacteriotropins, the essential basis for their 

 belief in the difference of the two groups of substances, at the time 

 being the relative thermostability of the bodies found in the immune 



