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SUMMARY OF CURRENT RESEARCHES RELATING TO 
this blood-serum other guinea-pigs can be immunized to the same degree 
in even less time (two months). 
Active immunity is developed 3 to 4 weeks after passive immunity 
becomes evident, and at first is very feeble. Forced immunization quite 
failed ; and to impart a high degree of immunity to these animals, guinea- 
pigs, it is necessary to use very small doses at first, and these must be 
very slowly increased, otherwise the animal’s life is in danger. 
No immunity was conferred on dogs by feeding them for a long time 
on guinea-pigs which had died of diphtheria ; nor was the result attained 
when the feeding was combined with treatment with heated cultures. 
The immunizing power of rat’s serum is less than that of guinea-pigs, 
while that of dogs is still greater. A powerful diphtheria poison is 
formed in bouillon cultures in 2 to 3 weeks, provided that the reaction of 
the pepton bouillon be made neutral to phenolphthalein. 
Effect of Citric Acid on Diphtheria Bacillus.* — After discussing 
the writings of numerous observers on the effect of citric acid on the 
bacillus of diphtheria, Dr. H. Laser gives his own experience. He found 
that 1 ccm. of 50 per cent, citric acid in 10 ccm. of diphtheria bouillon 
will kill the bacilli in 4-5 minutes. Inoculations with diphtheria bouillon 
cultures on the vaginal mucosa of guinea-pigs were made, and this 
was followed by touching up with 20 per cent, citric acid. The animals 
recovered so satisfactorily and rapidly that the author proceeded to try 
the effect on human beings. A 20 per cent, citric acid had neither a 
caustic nor a stringent effect. The solution was used as a gargle locally, 
and taken internally as a beverage. The results were encouraging. 
Sporicidal Action of Serum, j — Dr. J. Leclef selected the spores of 
Bacillus subtilis and those of the potato bacillus to work with in an 
investigation as to the sporicidal action of serum. The experiments 
were conducted in the usual way, and the author concludes from the 
results that rabbit’s serum, at any rate outside the body, rapidly and 
thoroughly destroys the spores of B. subtilis and those of potato bacillus. 
It loses this power if heated for an hour to 60°, and only exerts it in 
the presence of certain salts (sodium chloride). As the presence of 
nutritive substances does not impede the exercise of this function, it may 
be inferred that the death of the spores is not due to famine, but to the 
specific action of the serum. 
The same author X finds that there exists, at least in vitro , a close 
relation between the pathogenic power of microbes and their resistance 
to the destructive action of serum. This action was tested on ten dif- 
ferent micro-organisms, five pathogenic and five non-pathogenic. All 
the ten flourished if sown on heated serum. The tables show that the 
organisms decrease in virulence as follows : — Bacillus pyocyaneus , bacillus 
of rabbit septicaemia, Staphylococcus pyogenes aureus , Proteus , Bacillus 
coli communis , a red coccus, a putrefactive coccus, a yellow coccus, an 
undetermined bacillus, Bacillus subtilis. 
Further experiments showed that the relation between the virulence 
of microbes and their resistance to the bactericidal action of serum is 
manifested not only when a comparison is made between different 
* Hygien. Rundschau, 1894, p. 102. See Bot. Centralbl., lviii. (1894) p. 279. 
t La Cellule, x. (1894) pp. 347-74 (1 pi.). I Tom. cit., pp. 377-99. 
