RELATION OF LEUKOCYTES TO IMMUNITY 299 



A further method of investigation employed by Metchnikoff in 

 Ms endeavors to prove his point consisted in the attempt to demon- 

 strate that virulent bacteria could be protected from destruction in 

 the bodies of resistant animals if the leukocytes could be held at bay. 

 This resulted in a number of ingenious experiments, the most con- 

 vincing of which is the one carried out with anthrax bacilli and 

 frogs by Trapetznikoff. 7 Anthrax spores were inclosed in little sacks 

 of filter paper and these were introduced subcutaneously into frogs. 

 In consequence the spores, bathed in the tissue fluids, but protected 

 from phagocytosis, developed into the vegetative forms, multiplied, 

 and remained virulent for several days. Taken up by the frog's 

 phagocytes under ordinary conditions, they would rapidly have been 

 taken up, digested, and destroyed. Here again it was shown that the 

 body of fluids alone were unable to dispose of the bacteria and that 

 the natural resistance of the frog was due entirely to phagocytic 

 processes. 



Other experiments have been aimed at a general reduction of 

 phagocytic activity by the use of narcotics. Thus, Cantacuzene 8 

 showed that animals treated with opium are very much more sus- 

 ceptible to infection than are normal controls. And since opium 

 markedly inhibits the activity of the white cells it may possibly be 

 that these experiments furnish a further support for MetchnikofFs 

 opinion. At any rate, it is worth noting that, even though these 

 experiments are not convincing in their assertion that the increased 

 susceptibility was due entirely to the interference with the leuko- 

 cytes, they indicate very definitely the inadvisability of using mor- 

 phin and similar narcotics in infectious diseases. 



It is quite clear at any rate, then, that the process of phagocy- 

 tosis increases in energy as immunity is acquired and, so far, Metch- 

 nikofFs assertions are entirely upheld by later knowledge. In his 

 -contention that all properties upon which the resistance of the ani- 

 mal against infection depends center directly or indirectly in the 

 phagocyte, however, many subsequent amendments have been neces- 

 sary, which will become self-evident in the following discussions of 

 individual phases of the destruction of invading bacteria. 



We cannot at the present time attempt to correlate these extreme 

 views of Metchnikoff with the equally extreme opinions of those in- 

 vestigators who formerly attributed immunity entirely to the prop- 

 erties of the body fluids, assigning to the cellular activities a merely 

 secondary role. Many of the apparently opposed contentions have 

 become reconciled, and we now realize that neither process alone tells 

 the whole story, both being parts of the complicated correlated proc- 

 esses which together constitute the mechanism of resistance. It was 



7 Trapetznikoff. Ann. de I'Inst. Past., 1891. 



8 Cantacuzene. Ann. de I'Inst. Past., Vol. 12, 1898. 



