198 Relapsing Fever 
Manteufel (1908), in a further account of his investigations on 
relapsing fevers, showed that the virulence of any particular strain of 
spirochaetes is very much diminished by passage through a number of 
experimental animals, e.g. rats. He also found that animals which had 
recovered from a weakened strain of S. duttoni did not possess immunity 
against more virulent strains of the same parasite, but could be reinfected 
by them. 
These observations are of great interest for they show how careful 
one ought to be in distinguishing spirochaetes by their immunity 
reactions alone. There is little doubt that Fraenkel’s distinction 
between the East African and Congo strains of spirochaetes respectively 
may be explained by Manteufel’s I’esults, and therefore we propose to 
regard S. rossii, Xuttall, as synonymous with S. duttoni, Novy and Knapp. 
The two strains of spirochaetes are both transmitted, in nature, by 
the same intermediate host, 0. moubata, and produce very similar 
pathological effects in their vertebrate host, man. Moreover it is 
almost certain, from a consideration of the history and distribution of 
the disease (see below), that African Relapsing Fever was introduced 
into the Congo, from German East Africa, within comparatively recent 
times. 
As a further example of the uncertainty of distinguishing spirochaetes 
by their immunity reactions alone, may be mentioned Darling’s (1909) 
observations on the relapsing fever of Panama. Darling showed that 
“ infection by one strain of spirochaetes is followed by a considerable 
degree of active immunity for that strain, but such immunity is not 
potent against anot’ner strain from a different source although of the 
same species and from the same locality, but from a different human 
host.” 
Manteufel (1908) also found that S. recurrentis may be transmitted 
by 0. moubata, and more recently Neumann (1909) has shown that 
S. novyi may also be transmitted by the same means. 
Strong (1908) tried to obtain a serum reaction Avhich would enable 
one to diagnose African Relapsing Fever in the absence of spirochaetes. 
He found that the precipitin reaction was quite useless for diagnostic 
purposes, the only suggestion of a reaction being between N. novyi and 
African immune serum. 
Tedeschi (1910) has recently published an account of his investiga¬ 
tions on the biology of S. duttoni. He finds that the immune serum 
contains agglutinins which are destroyed by a temperature of 58° C. 
