PATHOGENICITY OF LEPTO. ICTEROHMMORRHAGIM FOR ANIMALS 921 



guinea-pig blood or liver, or rat-kidney suspension should be used. In subculturing, 

 0-5-1 ml. should be carried over to 5 ml. of fresh medium. The tubes should be incubated 

 at 25-30° C. ; growth occurs at 37° C, but degeneration rapidly sets in. Subcultures 

 should be made every 4 to 6 weeks, and kept at 25° C. The optimum pH for growth 

 is 7-6. The organism is aerobic ; in Noguchi's serum media, growth occurs at the top, 

 giving rise to a sUght haze, which stops abruptly a few centimetres from the surface. 

 Lepfo. icterohcemorrfiagice can also be cultivated on the chorio-allantoic membrane of the 

 developing chick embryo (Morrow et' al. 1938, Chabaud 1939). The organisms become 

 demonstrable in the blood of the allantoic artery in 4 or 5 days ; the embryo generally 

 dies within 7 days. Pure cultures of Lepto. icterohcemorrhagice may be obtained from 

 contaminated material by inoculating 0-5-1 -0 ml. intraperitoneaUy into a guinea-pig, 

 withdrawing blood by heart puncture ten minutes later, and culturing it in a suitable 

 medium (Schiiffner 1940) ; the leptospirse invade the blood more rapidly than the accom- 

 panying bacteria. 



Resistance. — Leptospira icterohcemorrhagioi is killed by moist heat at 50-55° C. in half 

 an hour ; it can withstand freezing. It is very sensitive to acid, being destroyed by 

 human gastric juice in 30 minutes ; it will not grow in an even slightly acid medium. 

 T'he organisms are rendered motionless in 10 to 15 minutes by 1/2000 HgClg and are gradu- 

 ally dissolved. They are rapidly destroyed by bile. In defibrinated blood kept at room 

 temperature in the light, the organisms remained virulent for 7 days, and in decomposing 

 liver for 27 hours (Uhlenhuth and Fromme 1916). In infected guinea-pig liver kept in 

 the ice-chest they remained virulent for 26 days (Buchanan 1927). 



Antigenic Structure. — Though it was thought at one time that there was but a single 

 species of Leptospira, namely Lepto. icterohmmorrhagire, further experience has revealed 

 the occurrence of several types differing in their antigenic structure, pathogenicity to 

 guinea-pigs, and the nature and severity of the disease to which they give rise in man. 

 Many of these types have been given specific names. The original icterohcemorrhagice 

 species can be distinguished antigenicaUy from other leptospiral strains that are pathogenic 

 for human beings. Its relation to water spirochsetes is still under discussion. Baer- 

 mann and Zuelzer (1928) found that water strains were not agglutinated by the sera 

 of convalescents from Weil's disease, or by the sera of animals inoculated experimentally 

 with Lepto. icterohcemorrhagice, and that sera prepared against avirulent water strains 

 did not agglutinate Weil strains. Brown and Davis (1927), using the adhesion test (see 

 p. 912), found that Lepto. icterohcemorrhagice from rats or man behaved alike, while Lepto. 

 biflexa was antigenicaUy distinct. Vaccination of guinea-pigs with cultures of Lepto. 

 biflexa failed to immunize them against Lepto. icterohcemorrhagice (Uhlenhuth and Zuelzer 

 1921). Accordmg to Baermann and Zuelzer (1928), however, some water strains, the 

 virulence of which has been raised by animal passage, behave antigenicaUy like Lepto. 

 icterohcemorrhagice. Some of the confusion is probably due to the lack of homogeneity 

 among water strains. The majority of these are saprophytes and belong to the species 

 Lepto. biflexa. Some of them, however, appear to be real icterohcemorrhagice strains, 

 either in their normal virulent condition or in a degenerate avirulent condition. Passage 

 through animals may succeed in restoring these to full virulence, rendering them indis- 

 tinguishable antigenicaUy from typical icterolicemorrhagice strains of parasitic origin. 

 Since animals not infrequently act as leptospiral carriers, it is possible that apparent changes 

 in antigenic structure and virulence brought about by passage are due to the isolation of 

 an organism from the animal different from that which was inoculated. Caution must 

 therefore be exercised in drawing conclusions from the type of evidence advanced by 

 Baermann and Zuelzer (1928) and Zuelzer (1930). 



Pathogenicity of Lepto. icterohsemorrhagise for Animals. 



Lepto. icterohcemorrhagice is highlj^ pathogenic for young guinea-pigs, whether given 

 intraperitoneaUy, subeutaneously, eutaneously, or by tlie mouth. The golden hamster is 

 likewise very susceptible (Morton 1942, Laison 1944). Rabbits, rats, and mice are only 



