// dependence on the constitution of the nutritive substrata may be 

 proved for parasites, naturally the strongest agent in combatting them is the 

 removal of the favorable nutritive substratum and its alteration into one un- 

 favorable for the special parasite. 



Since cultivated plants, by the fact of their division into susceptible and 

 resistent varieties, demonstrate that there is a possibility of altering the nutri- 

 tive substratum i)roduccd by living plants, the production of such resistent 

 individuals through cultivation is the first aim of our work, in regard to 

 overcoming parasitic diseases. It is more eflfective than the present method 

 of fighting parasites locally or preventing their attacks, a method which was 

 deduced from a narrow point of view. At most this may be carried through 

 cflfectively for small centres of disease but for mechanical reasons is im- 

 practicable for general use. From this point of view parasitism is not such 

 a great menace as it has been represented to be. 



If parasitism is a definite nutritive form of certain groups of organisms 

 which has become necessary in the natural development of the living being, 

 it must have its stage of equilibrium in the sphere of nature. Arrangements 

 must exist which counterbalance parasitism. It must be possible to hinder 

 its efifcctiveness by factors simultaneously effective, for otherwise the nutri- 

 tive organisms could no longer exist. This counterbalance is found in 

 the very definite, often narrowly restricted environment which determines 

 the existence of the parasite. That condition of a living creature which we 

 are accustomed to term "healthy," without being able as yet to define it, is 

 one such restricting limit which the parasite under normal conditions is not 

 able to overcome. For, since the defenders of the extreme theory have 

 represented such parasitic micro-organisms as dangerous which are con- 

 stantly present everywhere saprophytically and as yet have not killed the host 

 plants as a whole, these plants must thus possess some protective devices in 

 their normal development, which are repeated in the same sense from gene- 

 ration to generation. We constantly find occurring as such, unbroken de- 

 posits of wax and cork, definite acidity of the cell content etc. 



That we now find more and more adherents to our theory is proved by 

 the statements of one of our most important students of parasitism, Met- 

 schnikoff^ of the Pasteur Institute. After giving a number of examples 

 to show that the production of the parasitic disease is conditioned by 

 tzvo causes, first, the parasite and secondly, susceptibility of the organisms, 

 he says, (page 7) "if these internal conditions are powerless to arrest the 

 development of the excitor of a disease, the disease is produced. If, how- 

 ever, the organism firmly resists the development of the bacteria, it is pro- 

 tected and thus proves itself immune." (Page 6) "One can no longer be of 

 the opinion that, every time an excitor of disease penetrates a susceptible 

 organism, the presence of the same inevitably calls forth this specific dis- 

 eased condition. Loffler's discovery of the diphtheria Bacillus in the pharynx 



1 Immunittit bei Infektionskrankheiten by Elias Metschnikoff, Professor of the 

 Pasteur Institute in Paris. Authorized Translation by Pr. Julius Meyer. Jena, 

 Gustav Fischer, 1902. 



