PROTECTIVE INOCULATIONS. 369 
repeated injections of sterilized (by heat) cultures. The authors last 
named have also tested the blood serum of typhoid-fever patients, of 
recent convalescents from the disease, and of persons who had sutf- 
fered an attack some years before the experiment was made. The ex- 
periments were made upon guinea-pigs. The authors conclude that 
‘in general the guinea-pig is immunized against the action of virulent 
typhoid cultures by the subcutaneous injection of a small quantity 
of serum of persons who have suffered an attack of the disease, no 
matter how remote.” But this immunity was shown to be of short 
duration, and quite different from that induced by the injection of 
sterilized cultures, which does not immediately follow the introduc- 
tion of the toxic substances, but requires a certain number of days for 
its development. The degree of immunity is said by the authors last 
named to depend to a considerable extent upon the dose given, and 
the animals treated in this way still resisted virulent cultures at the 
end of two months. On the other hand, injections of blood serum 
from immune individuals were effective in doses of a single cubic cen- 
timetre, within a few hours, and the immunity conferred had a com- 
paratively brief duration. 
Protective inoculations in man have been practised on quite a large 
scale by surgeons of the English army in India and in South Africa. 
The method of Wright has been followed in preparing sterile cultures 
for inoculation. Cultures in bouillon are made and kept in the incu- 
bator at 37° C. for two or three weeks. The cultures are then drawn 
into small glass tubes, which are sealed by heat. The tubes are 
placed in a vessel containing cold water, and the temperature is grad- 
ually raised to 60° C., where it is maintained for five minutes. Plant- 
ings in a culture medium are made from these tubes to make sure that 
sterilization is complete. As a further protection against the intro- 
duction of living bacteria, one-half per cent of lysol may be added to 
the sterilized culture. The amount used for protective inoculations 
in man has been fixed at two-fifths of the minimum amount, which 
would be fatal to a guinea-pig weighing two hundred and fifty 
grammes. The inoculation gives rise to a well-marked local reaction, 
which does not result in suppuration, and to more or less pronounced 
general disturbance. Usually this is slight, but sometimes rigors, 
nausea, and a tendency to syncope occur. That these inoculations 
are not without effect is shown by the fact that the blood serum of 
an inoculated individual exercises a marked agglutinating action 
upon the typhoid bacillus in a recent culture (Widal reaction). This 
is said to be equal to that resulting from an attack of typhoid fever. 
Cameron, after an inoculation practised upon himself, found that at 
