gradually clearer that small living creatures, in fact, the smallest which are 

 intHKluced by means of articles of commerce or can be easily distributed by 

 dust and wind, may be kept out of small enclosed places but not away from 

 extensive open localities, and that one proceeds better by presupposing the 

 possibilities of a widespread distribution of such organisms although real 

 danger is to be recognized only if an easy capacity for its increase has been 

 proved. If now in all parasitic incursions, not the presence of the parasite 

 but the conditions favoring its spread are proved decisive for the production 

 of the epidemic, then a change in these conditions is the best means for com- 

 batting them. 



In regard to measures for its suppression and prevention, however, the 

 epidemic furnishes special pointers in that, when it occurs over extensive 

 areas, it excludes as causes all the factors which vary from one another in 

 the difYerent diseased districts. For, since the malady attacks large plan- 

 tations despite the variation? in such factors as, for instance, situation, com- 

 position of the soil, agricultural methods etc., these factors cannot be the 

 cause. Rather the cause should be sought in those influences which are the 

 same throughout the whole country. Actually, this can only be the climate. 

 On the other hand, in endemic diseases, conditions of the soil usually act de- 

 cisively. They are to be considered either direct causes of disease since, 

 through unfavorable chemical or physical pculiarities they permanently dis- 

 turb the functions of the plants, or they act indirectly, favoring the increase 

 of the parasites and the strength of their attacks. In this, as a rule, they 

 .suppress at the same time the growth energy of the host plant. Soil damp- 

 ness is the condition most favoring this. When the capacity of thick, heavy 

 soils for retaining water is very great on the level or in hollows, an accumu- 

 lation usually occurs which finds no outlet and produces a deficiency of oxy- 

 gen, with an excess of carbon dioxid. The plants indicate this functional 

 disturbance by a change in the chlorophyll apparatus. The leaves, gradually 

 turning yellow, form a suitable growing medium for certain groups of fungi. 



In all endemics and epidemics a simultaneous sickening of a great num- 

 ber of individuals indicates a considcvahlc period of prcpamtioii Jcadiii;/ up 

 to the actual outbreak of the mahidy. 



For, according to our conception of all the phenomena of life as dynamic 

 processes, each case of disease may be characterized as the immediate or in- 

 direct result of mechanical disturbances exercised by the separate factors of 

 growth on the composition and function of the substance. The life of a cell 

 is a constant struggle between the oscillatory forms momentarily present in 

 the unstable organic compounds and the disturbances constantly exercised 

 upon them ])y the factors of growth. 



A change in the substance and with it one in its function appear at 

 once if the disturbance in one factor of growth is so strong that it is able to 

 change the form of oscillation existing up to that time. So long as the dis- 

 turbances as a whole have the effect of contributing to the development of 

 the organism as a whole, that is, the vegetable individual, the plant remains 



