EFFICACY OF HAFFKINE'S PLAGUE PROPHYLACTIC 
21 
Another experiment was made in which the supernatant fluid in the broth acted upon by 
the microbe was separated from the sediment of microbes, and the two constituents tested separately 
and together with respect to their prophylactic properties. 
Experiment IV 
A 2 1 -day-old broth culture, obtained recently from a patient, was filtered through a porcelain filter, 
and the microbes remaining on the candle of the filter were washed oft' into a quantity of sterilized water, 
equal in amount to the broth of the culture taken. The suspension was heated at 60° C. for thirty 
minutes. Rabbits were inoculated as follows : 
No. Weight. 
1 ... 1,750 grams inoculated with 3 c.cm. filtrate. 
2 •■• 1,150 M " 3 
3 ... 1,150 „ ,, ,, 3 „ suspension. 
4 ... 1,610 „ „ „ 3 „ ,, 
5 ... 1,150 ,, „ „ 0.75 ,, filtrate, 0.75 c.cm. suspension. 
6 ... 1,150 ,, ,, ,, 0.75 ,, „ 0.75 ,, „ 
Immediately after they were inoculated in the other flank with of a suspension of a 3-days-old 
agar culture of plague obtained from the same broth culture. Two controls were also inoculated with the 
same quantity of the living culture alone. The controls both died, one in forty-eight hours, the other in 
three to four days ; a large number of bacilli were found in the heart blood. 
Nos. I and 2 both survived, but No. I was 111 for 6 days. 
No. 3 died in 3 days, but very few bacilli were found in the heart blood, either by the micro- 
scope or by cultivation. 
No. 4 survived. 
No. 5 died In 49 hours, but no plague microbes were found In the heart blood, so it cannot be said 
to have died of plague. 
No. 6 survived. 
It appears from this experiment that the filtrate alone conferred power to prevent or to 
modify an attack of plague ; Rabbit No. i probably had plague, but survived. 
The suspension of sterilized microbes seems to Iiave conferred bactericidal properties, for 
the blood of the Rabbit No. 3 contained few bacilli compared to that of the controls. 
The mixture of filtrate and suspension of sterilized microbes protected Rabbits Nos. 5 and 6 
from plague infection, for no plague bacilli were found in the blood of Rabbit No. 5. The dose of 
the mixture was equivalent to 0.75 c.cm, of culture; this dose was taken and not 1.5 c.cm., as 
appeared from the first experiments to be required, because in this last experiment older, and 
therefore stronger, culture was used. 
LusTiG and Galeotti* state that the immunizing property is a nucleo-proteid contained 
in the bodies of the microbes, and that if Haffkine's prophylactic has any immunizing property 
it is due to the nucleo-proteid dissolved or still contained in the bodies of the microbe. But this 
would not obtain in the above experiments, for the cultures were made in slightly acid broth— 
that is, ordinary beef broth without the addition of an alkali, so the nucleo-proteid would not be 
dissolved. Moreover, the cultures used were young and the microbes probably all living and not 
in a state to give up their nucleo-proteid. 
* 'British Meilical Journal,' February lotli, 1900. 
