196 
Relapsing Fever 
Breiul and Kinghorn (1906 b) were the first to publish an account 
of the immunity reactions of S. duttoni in experimental animals. 
They showed that, with the exception of cats, all the common laboratory 
animals may be infected by inoculations, but that the most susceptible 
are white rats and monkeys. It was found that after recovery from 
an infection animals possess a “ relatively active immunity against 
reinfection,” as previously shown by Gabritschewsky (1905) in the case 
of European Relapsing Fever, but that immune serum had no appreciable 
effect in preventing, or curing, the disease in other susceptible animals. 
In some cases the incubation period was prolonged when the inocula¬ 
tion had been foliow'ed by an injection of immune serum, but the 
severity of the attack was not appreciably diminished. On the other 
hand, an injection of hyperimmune serum, besides prolonging the 
incubation period, mitigated the severity of the infection and occasionally 
cut short the attacks. They also found that the spirochaete of the 
Relapsing Fever of Tropical Africa differed from 8. recurrentis in its 
immunity reactions, for animals which had recovered from the former 
were liable to infection with recmirentis, and vice-versa. 
The same authors (Breinl and Kinghorn, 1906 a) showed that 
8. duttoni is capable of passing through the placenta and infecting 
the foetus; and that the young of an infected mother are born with a 
slight immunity which is of short duration. 
Novy and Knapp (1906) gave a complete account of all previous 
work on spirochaetal infections and also the results of their own investi¬ 
gations of 8. recurrentis, especially with regard to its serum treatment 
on the lines suggested by Gabritschewsky (1905). The results they 
obtained by treating animals infected with recurrentis with hyper¬ 
immune serum were very favourable, and led them to make the 
statement that they had established “ a sound basis for the prevention 
and cure of relapsing fever and the related tick-fever.” The results of 
Breinl and Kinghorn, however, do not support this statement as far as 
the latter disease is concerned. 
Uhlenhuth and Haendel (1907) differentiated the spirochaetes found 
in European, African and American Relapsing Fevers, respectively. 
They confirmed the previous observation that infection with any 
particular strain is usually followed by immunity against the same 
strain, but not against other varieties. If hyperimmune serum be 
brought in contact with blood containing spirochaetes of the same 
strain, a well-marked agglutination takes place and the parasites lose 
their motility within about half an hour, and undergo granular disinte- 
