PROTECTIVE INOCULATIONS. 295 
with a culture of this spirillum are subsequently immune against the 
pathogenic action of the cholera spirillum, and vice versa. In subse- 
quent communications Gamaleia reported that sterilized cultures of 
his “Vibrio Metchnikovi” (sterilized by heat at 120° C.) were very 
pathogenic for rabbits, fowls, pigeons, and even for dogs and sheep. 
The rabbit proved to be the most susceptible animal, and succumbed 
to doses of four cubic centimetres in from twelve to twenty hours. 
Doses of one cubic centimetre per one hundred grammes of body 
weight caused a temporary indisposition followed by immunity. 
Pigeons were made immune by larger doses. 
The researches of Pfeiffer (1889) confirmed those of Gamaleia as 
to the fact that pigeons and guinea-pigs could be made immune 
against Vibrio Metchnikovi by the injection of sterilized cultures. 
But guinea-pigs which had been immunized against this pathogenic 
spirillum succumbed to cholera infection; and, on the other hand, 
animals which had been treated in various ways with a cholera cul- 
ture died without exception when infected with Vibrio Metchnikovi. 
The conclusion is therefore reached that the two pathogenic spirilla 
are distinct species, although very similar in many respects. 
Brieger and Wassermann (1892) have reported the results of ex- 
periments with the cholera spirillum cultivated in thymus bouillon. 
After twenty-four hours’ development in this medium the cultures 
were sterilized by heat (55° C. for fifteen minutes) and placed in an 
ice-chest for twenty-four hours. Four cubic centimetres of this fluid 
injected daily for four days into the peritoneal cavity of a guinea-pig 
made it immune to the cholera spirillum in doses three times as large 
as were required to kill an animal not so treated. This immunity 
lasted for two months. Fedoroff (1892) obtained similar results by 
the subcutaneous injection of sterilized cultures in doses of one cubic 
centimetre, in guinea-pigs. His cultures in thymus bouillon were 
kept for from seven to ten days at 37° C., then sterilized by heating 
for fifteen minutes at 65° C., then allowed to stand in a dark room for 
twenty-four hours, and finally mixed with an equal volume of glycerin. 
‘Ketscher (1892) has obtained evidence that the immunizing sub- 
stance in animals which have received protective inoculations is con- 
tained in the milk of females thus treated. Three goats received 
subcutaneous inoculations of virulent cholera cultures, and also injec- 
tions into a vein and into the peritoneal cavity. The milk of these 
goats was injected into the peritoneal cavity of rabbits; these proved 
to be immune when subsequently lethal doses of a virulent cholera 
culture were injected into the peritoneal cavity. 
According to Gamaleia (1892), dogs are very susceptible to infec- 
