594 TREPONEMATA, SP I RON EM AT A, LEPTOSPIRATA 
to monkey, and from monkey to mice and rats, which are all suscep- 
tible. Rabbits and guinea-pigs appear to be refractory. The disease 
produced by inoculation of the organisms in monkeys and mice exhibits 
the characteristic relapses, and it may be fatal. 
Fig. 82. — Spironema recurrentis. (Kolle and Hetsch.) 
Hvman.—TheTQ are no characteristic lesions observed in relapsing 
fever other than a hyperplastic enlargement of the spleen. There 
may be a catarrhal inflammation of the stomach, bile ducts and liver, 
which is usually enlarged. All of the organs exhibit parenchymatous 
degeneration postmortem. 
Bacteriological Diagnosis.— The organisms are found in the blood 
stream only during the paroxysms. During the period of apyrexia 
they disappear from the blood stream, but are found in the spleen 
in large numbers, where they are engulfed by leukocytes. 
Immunity.— According to Novy,i blood drawn from a patient at 
the beginning of the fever acts as a good culture medium for the 
organisms ; that drawn at the end of a paroxysm or after recovery from 
the disease appears to possess germicidal properties for the organisms. 
It is supposed that the organisms are taken up by phagocytes during 
the afebrile periods, and that they are either weakened or killed at 
this time. Active immunity follows recovery from the infection. It 
has been claimed that the blood serum of immunized animals (which 
exhibit immunity after repeated injections of the organism) or of 
animals which have recovered from an attack will induce passive 
immunity and temporarily prevent infection when it is introduced 
into susceptible animals prior to inoculation of the organisms. 
Transmission.— The disease appears to be transmitted by suctorial 
insects. IVIackie^ believes the human louse, Pediculus vestimenti, is 
commonly the one involved, but ManteufeP has produced evidence 
suggesting the rat louse, Hematopinus spinosus, is at times a carrier 
of the organism. 
I Jour. Infec. Dis., 1906, 3, 291. 2 British Med. Jour., 1907, ii, 1706. 
3 Arb. a. d. kais. Gesamte, 1908, 39, 355. 
