468 SPIRILLUM CHOLERA ASIATICS. 



Von Pettenko- Von Pettenkofer admits that in the case of cholera 

 s view. we | iave f. do w j^ a v i rus w hich is carried from place 

 to place, but he lays chief stress on the facts as to the 

 peculiar local and seasonal distribution of cholera, and 

 he assumes that in addition to the virus introduced, 

 other factors, dependent on the locality, must come into 

 play in order that an epidemic should occur. If we 

 call the virus which proceeds from the patients " x," 

 and the something due to the locality " y" cholera only 

 spreads when x and y occur together ; x alone can only 

 quite exceptionally cause a single case of the disease, 

 but never an epidemic. On the contrary, in a place 

 where y is absent we may swallow cholera dejecta with- 

 out any harm ; while an infection would follow under 

 these circumstances if y was present in the same 

 locality. 



Pettenkofer has attempted to ascertain the nature of 

 ;/ by an accurate investigation of the local and seasonal 

 distribution of a large number of cholera epidemics, and 

 he has come to the conclusion that the nature of y is a 

 certain character of the upper layers of the soil. A soil 

 which predisposes to the disease must be porous and 

 penetrable by air and water, it must be contaminated 

 with dejecta, organic substances, &c., and it must be to 

 a certain extent moist. The moisture of the soil is the 

 factor which chiefly varies with the season ; too great 

 moisture diminishes the predisposition in the same 

 manner as too great drought. The degree of moisture 

 of the soil is in the majority of cases most accurately 

 shown by the variations in the level of the ground-water, 

 in other cases it is better determined by the amount of 

 rainfall. 



Hence those localities are permanently immune where 

 the ground is composed of rock or dense clay, also those 

 where the soil is quite clean, and those where the sur- 

 face of the soil is always either very dry or very moist. 

 A temporary immunity is occasioned chiefly by too 

 great or too little moisture of the soil. 



According to Pettenkofer' s view the relation between 

 the virus x and the factor y, which depends on the pre^- 



