296 PROTECTIVE INOCULATIONS. 
tion with cholera spirilla, and present symptoms closely resembling 
those of cholerain man. They may also be easily immunized against 
the pathogenic action of cholera cultures. 
Gruber and Wiener (1892) have also found that susceptible ani- 
mals are easily immunized against cholera infection either by inocu- 
lation with small doses, with attenuated cultures, or with larger quan- 
tities of sterilized cultures. Haffkine (1892) also reports his success 
in immunizing guinea-pigs and pigeons. 
Pawlowsky (1893) claims to have obtained from the blood of ani- 
mals having an acquired immunity against cholera an antitoxin in the 
form of an amorphous powder; and Lazarus (1892) reports that the 
blood of man, after recovery from an attack of cholera, has the prop- 
erty of protecting guinea-pigs from fatal infection when injected, in 
very small amount, into the peritoneal cavity. Issaeff (1894) in an 
extended series of experiments was not able entirely to confirm the 
results reported by Lazarus. In a summary of results obtained in 
his own experiments he says: 
“1. The intraperitoneal or subcutaneous injection of blood serum from 
normal individuals [that is, persons who have not suffered an attack of 
cholera], and also of various acids, alkalies, and neutral liquids, gives to 
guinea-pigs a certain resistance against intraperitoneal cholera infection. 
This resistance, however, is feeble and temporary, aud cannot be considered 
as identical with the true immunity which results from vaccination with the 
products of the cholera bacteria. 
‘*2. Guinea-pigs vaccinated against cholera have no immunity against 
the toxins of the cholera vibrio, notwithstanding their high degree of insus- 
ceptibility to infection with cultures containing the living vibrio. The blood 
of immunized guinea-pigs does not possess antitoxic properties. The maxi- 
mum dose of cholera toxins which immune guinea-pigs can withstand is not 
greater than that which control animals withstand. : 
‘3. The blood of guinea-pigs carefully immunized against cholera pos- 
sesses specific and very pronounced immunizing, and, in a certain sense, 
curative powers. 
‘‘4, The blood of cholera convalescents possesses similar specific and 
curative powers. This property is first developed about the end of the third 
week oo the attack, and disappears completely at the end of two or three 
months.” 
In a series of experiments made by Pfeiffer and Issaeff the results 
obtained, as stated by Pfeiffer in a subsequent communication, were 
as follows: 
‘‘In my research with Issaeff ‘upon the explanation of cholera immu- 
nity’ I proved that the serum of animals which have an active acquired im- 
munity against cholera only has a specific action upon this particular species 
of vibrio, and as regards other species of bacteria does not differ in its action 
from the blood serum of normal animals. We also showed that this specific 
influence in respect to the intraperitoneal cholera infection of guinea-pigs 
was due exclusively to bactericidal processes which in some way were in- 
duced by the serum of immune animals.” 
