19 



of healthy children has been repeatedly substantiated since that time and yet 

 it is impossible to doubt the etiological significance of this bacillus for diph- 

 theria. On the other hand it has been proved that Koch's Vibrio, although 

 the real incitor of Asiatic cholera, nevertheless, occurs in the digestive system 

 of healthy people." 



The healthy organism thus possesses a natural immunity and any distur- 

 bance of this aids the possible parasitic attack. 



5.* Epidemics. 



If we can define endemics as a local malady, whose production is con- 

 nected with definite conditions, narrowly limited locally, then epidemic may 

 be called a community malady. The expression "malady" indicates the mul- 

 tiplicity of the diseased individuals in contrast to isolated cases of disease. 

 Epidemic thus describes that condition in which numerous individuals suc- 

 cumb to a given form of disease, developing over large territories. 



If an epidemic breaks out, conditions must be present which disturb the 

 functions of the organism in numerous individuals so strongly that .their 

 lives are either threatened with a premature end or are finally brought to 

 this end. This disturbance arises from external causes. If these causes are 

 parasitic organisms, their existence, as was shown in the preceding chapter, 

 is dependent on the factors of growth favorable to their extensive increase. 

 Among these factors belongs the breaking down of the immunity of the 

 nutritive organism. 



Even with the assumption that a parasite not indigenous to the countries 

 which suffer from the disease might have caused the epidemic by its incur- 

 sion, this circumstance in no way changes the fact that the factors of growth 

 already existing are determinative for the production of the epidemic. For. 

 whatever may wander into the country, be it animal, fungus or bacterium, 

 this incursion would not produce an epidemic, if the newcomer found no 

 opportunity for great increase and wide distribution. For example, who 

 does not remember very effective representations of the importation of the 

 Colorado beetle as the destroyer of our potato crop, or the extensive intro- 

 duction of the San Jose scale as the destroyer of our fruit trees? Initiated 

 persons know how often embargo regulations and compulsory disinfection 

 have advanced protection against the importation of parasitic fungi ("White 

 Rot of the Grape" etc.) and they have partially succeeded in getting it. 



Experience has taught that no theoretically imagined but practically im- 

 possible complete destruction or quarantine of such parasites has possibly 

 protected us from epidemics but the circumstance that they did not find the 

 necessary climate and soil for their increase. Conversely, the Phylloxera 

 plague should be remembered which, despite all human endeavor and the 

 spending of many millions, became more and more widespread. The 

 Phylloxera finds, even in Europe, sufficiently favorable conditions for exis- 

 tence and on this account defies such means for fighting it as embargo, dis- 

 infection, processes of extermination etc. Upon consideration, it becomes 



