602 TREPONEMATA, SPlRONEMATA, LEPTOSPIRATA 
sera, however, prepared by injections of Leptospira icteroides into 
suitable animals were found to agglutinate this organism, but not 
Leptospira icterohtemorrhagia?. Complement-fixation was less dis- 
tinctive. 
A polyvalent serum^ of high potency was found to possess protective 
power against infection with Leptospira icteroides in guinea-pigs, 
especially in the earlier stages of the disease. Xoguchi has used 
vaccines containing 2 billion leptospirata for preventive inoculation 
with promising results. Also, he has prepared a serum by immunizing 
horses, which has distinct curative value, provided it is given within 
the first three days of the clinical disease.- 
Filterability.— According to Noguchi,^ the Leptospira will pass the 
pores of a Berkefeld V and N filter, and yet retain its infectivity. 
Wolbach and Dinger,* Novy and Knapp,^ and Breinl and Kinghorn,'^ 
have observed that spirochetes may pass through the coarser Berke- 
feld filters (which will restrain B. prodigiosus) and yet retain their 
viability. It is not clear whether the plasticity of the organisms per- 
mits of their passage through the tortuous spaces of the filter or 
whether, as Balfour^ and Leishman^ have suggested, there may be a 
fragmented or granular stage in the life history of spirochetes which 
is of sufficient minuteness to permit of passage. In this connection, 
it may be recalled that gummata from syphilitics frequently show no 
Treponemata, yet they are infectious for monkeys. 
DENGUE. 
The etiology of dengue has not been definitely established, but it 
appears to belong to the group of filterable viruses and was supposed 
to be transmitted by Culex fatigans, a mosquito very common in the 
tropics. Graham^ claimed to have transmitted the disease to non- 
immune individuals not only through the bite of infected female Culices, 
but also by injecting the ground up salivary glands of a mosquito that 
had previously bitten a patient. Ashburn and Craig^° state that the 
virus will pass a Berkefeld filter and that both whole blood and serum 
filtered through Berkefeld filters will reproduce the disease in non- 
immune individuals. The incubation period in these cases was about 
four days. 
Bancroft'^ has transmitted dengue to non-immunes by female yellow 
fever mosquitoes (Aedes aegypti). At least twelve days must elapse 
1 Noguchi: Jour. Exp. Med., 1920, 31, 159. 
2 Noguchi: Jour. Trop. Med. and Hyg., May 15, 1925. 
3 Jour. Exp. Med., 1919, 30, 13. 
•" Jour. Med. Res., 1914, 30, 9, 23. Wolbach: Am. Jour. Trop. Dis. and Prev. Med., 
1915, 2, 494. 
s Jour. Infec. Dis., 1906, 3, 375. 
6 Mem. XXI, Liverpool School Trop. Med., 1906, vol. 1. 
7 Internat. Cong. Med., 1913, 21, 275. « Ibid., p. 282. 
9 Jour. Trop. Med., 1903, 6, 209. " Philippine Jour. Sci., 1907, 2, 71. 
'1 Australasian Med. Gaz., 1906, 25, 17. 
