27 



8. Predisposition and Immunity. 



In an earlier part we have pointed out that our theory as to the produc- 

 tion of parasitic diseases has obtained support from the most renowned in- 

 vestigators. Metschnikoff^ who, as professor in the Pasteur Institute 

 for infectious diseases, may be incontestibly considered as an exact con- 

 noisseur of pathogenic micro-organisms, expresses himself as follows, 

 "Exact bacterialogical mvestigations have led to the knowledge that, in the 

 abundant bacterial flora harbored by the healthy human body, representa- 

 tives of pathogenic bacterial species may also be found. Aside from the 

 Bacillus of diphtheria and the Vibrio of cholera which so often have been 

 proved to be fully virulent in perfectly healthy human beings, it has been 

 shown that certain pathogenic micro-organisms, the Pneumococci, the Sta- 

 phylococci, Streptococci and Colibacilli, are present regularly or almost con- 

 stantly in the microbe flora of healthy persons. 



This discovery has of necessity led to the conclusion that besides the 

 excitor of the disease, still a seeond cause of infectious diseases must exist, 

 namely, a predisposition or a lack of immunity. An individual which harbors 

 one of the species of pathogenic bacteria above-named would be resistant 

 either permanently or for the time being. But as soon as this immunity dis- 

 appears, the excitor of the disease becomes uppermost and produces the 

 specific disease." 



In regard to the immunity of plants, Metschnikoff calls attention to the 

 investigations of de Bary^ on Botrytis, which we have already men- 

 tioned. The mycelium of this fungus penetrates the cell walls by giving oft' 

 a fluid "which contains a digestive ferment and the oxalic acid necessary for 

 this ferment. De Bary could prove the presence of this kind of toxin by the 

 maceration of the mycelium of Sclerotinia .... If the resulting fluid 

 is heated to 52°C. it can no longer digest the cellulose membrane but is still 

 able to cause plasmolysis .... The results of de Bary's investigations 

 have been confirmed and in part completed by Laurent.'"'^ 



We have repeated JNTetschnikoff's words in order to characterize his 

 way of considering the matter. The chief factor under consideration here, 

 viz., the eft'ectiveness of the ferment on young membranes and its ineft'ective- 

 ness on older ones, gives the author reason for comparing the Botrytis dis- 

 eases with the infantile diseases in human beings (measles, scarlet fever). 

 In other cases the different processes of cork production, or suberization, 

 found, for example, in wounds, act in a way similar to the membrane changes 

 in the ageing of the cells. In regard to these, Metschnikoff, supported by the 

 investigations of Massart^ points out that the organs respond differ- 

 ently to the traumatic stimulus according to their age. Young leaves of 

 Clivia, for example, re-act by forming callus, older ones simply close the 



1 MetsclinikofE, Immunitat bei Infectionskrankheiten. Jena, 190' 



2 De Bary Bot. Zeit. 1866. 



a Laurent, Annal. de I'Institut Pasteur. Vol. Xlll, p. 44. 

 •i Massart, La Cicatrisation chez les plantes. Brussel 1897. 



