478 ISHIZUKA ; ON THE SIGNIFICANCE OF THE NITRATES 
He has also called attention to his observation, that great 
cholera epidemics appear in those years in which the rain fall 
of summer remains far below the average, which fact would 
appear very strange, if the cholera bacillus alone were the 
cause, as abundance of moisture would be most favourable to 
the development of that bacillus. (,) This fact as well as the 
gradual decrease of the epidemic towards winter, 1 (2) and further its 
breaking out at the time when the new vegetables are harvested, 
is in best accordance with the theory of Emmerich and Tsuboi, 
for which my own investigations above described bring further 
support. Finally I must point out that the law, discovered by 
Pettenkofer in regard to the influence of rain, is also confirmed 
by the phenomena observed in Japan : I compared the intensity 
of the four cholera epidemics during the last 13 years with the 
amount of rain-fall from May to October, and from this it becomes 
evident that in those years in which the rain fall was considerably 
below the average, the epidemic was more serious than in those 
years in which the rainfall was more copious, as the following 
tables show : 
(1) I do not assert here that the nitrites produced are the exclusive poison in cholera. 
Indeed Hüppe and Scholl have discovered in cholera cultures also poisonous proteids. 
There exist cases of a milder form of cholera in which the formation of nitrites is not the 
leading factor, as, eg., also the cholera produced in Guinea-pigs by subcutaneous injec¬ 
tions of comma bacilli, Cf. also the interesting article of Hüppe , Terl. Klin. Wochenschr. 
1894. No. 17. 
(2) Montefusco tries to explain this by the decreasing virulence in great cold, but 
this is not satisfactory, as cholera stops even in warm winters. 
