PHAGOCYTOSIS 61 



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 preparatory 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 

 phagocytosis 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 contradistinc- 

 tion to Metschnikoff, 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 bacterium in the sense that the exo- and endotoxins of the 

 latter were neutralized 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 

 leukocytes to serum and subsequent washing gave rise to negative 

 results. Wright and Douglas hence termed the substances in question 

 opsonins (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 

 regarding the presence of prophagocytic 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 



