344 PA THOGENIC BA CTERIA.
The opinion of the writers is that '(the only trust-
worthy difference between many of these varieties and
the true cholera spirillum is the specific reaction with
serum from animals immune from cholera, or by Pfeiffer's
method of intraperitoneal testing in such animals.''
In discussing these spirilla of the Philadelphia waters
4 c The most important point with regard to the occur-
rence of these organisms in the river water around Phil-
adelphia, is the fact that similar organisms have been
found in the surface-waters of the European cities in
which there had recently been an epidemic of Asiatic
cholera, notably at Hamburg and Altona. . . . The fore-
most bacteriologists of Europe have been inclined to the
opinion that the organisms which they found in the sur-
face-waters of the European cities were the remains of
the true cholera organism, and that the deviations in the
morphologic and biologic characters from those of the
cholera organism were brought about by their prolonged
existence in water. No such explanation of the occur-
rence of the organisms in Philadelphia waters can be
1 Jour, of the Amer. Med. Assoc., Oct. 23, 1897.