SPIRILLUM CHOLERA ASIATICS. 449 



from the facts as to the mode of spread of cholera has Differences h 

 been that the mode of infection in this disease is ousness oP" 

 essentially different from, and more dependent on, ex- cholera and 

 ternal influences than in the case of other infectious 

 diseases, for example in small-pox. And this experience 

 is quite intelligible if we bear in mind that in small-pox 

 there are none of those marked limitations in the 

 mode of spread of the virus which are seen in cholera. 

 In the case of small-pox we have a much greater 

 multiplicity of the sources of infection on account 

 of the fact that the virus is given off from the whole 

 skin in the remains of the pustules, and that it is con- 

 tained in the various secreta ; we have also to do there 

 with much more resistant infective agents, which evi- 

 dently withstand drying, and can be carried by currents 

 of air and dry objects ; hence the facilities for the 

 penetration of the contagium into the body are very 

 great ; apparently also the protective arrangements in 

 the body which render the poison inactive even after 

 its entrance have much less power. Hence the 

 spread of small-pox by contagion is so very different 

 from that of cholera, and the mode of spread of cholera 

 acquires a special character from the fact that so many 

 external influences render its diffusion difficult in certain 

 cases. 



In the dependence of cholera infection on external Value of 

 influences we have the explanation of the fact that in- SS cti 

 dividuals can be so easily and completely protected against 



., . ,. , ., cholera. 



against tins disease, much more easily than against 

 scarlatina and small-pox. While in the latter cases all 

 the numerous and permanent sources of infection can 

 scarcely be attended to, and while the usual mode in 

 which the virus enters, namely, by the respired air, 

 cannot be controlled or influenced, it is by no means so 

 difficult to exclude completely the possibility of the 

 transmission of cholera. If the dejecta and the objects 

 soiled by them are cleansed and disinfected all the sources 

 of infection are got rid of ; if the hands, food, and drinking 

 water are kept quite clean the most important contami- 

 nated sources are shut off; if all gastric disturbances are 



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