The observed similarities and minor differences between the relapsing fever spirochete found in Texas and the strains observed elsewhere may be summarized as follows:
1.The Texas spirochete presents no essential differences in morphology from the known varieties.
2.Viability in vitro depends to a great extent upon time in the disease when blood is taken.
3.Freezing temperatures of 2 per cent sodium citrate—0.8 saline solutions kill the spirochete.
4.Fifty-two degrees Centigrade for twenty minutes is more than the actual thermal death point.
5.The Texas spirochete does not pass a Berkefeld N candle nor a Seitz filter at 40 mm. negative pressure.
6.In our hands, cultivation was unsuccessful in Noguchi's medium and in blood and serum mixtures both under aerobic and anaerobic conditions.
7.Virulence may be greatly increased by rapid transfer of onset blood.
8.White rats, white mice and rhesus monkeys are quite susceptible to the Texas spirochete. Their reactions present no essential differences from those observed in the same kind of animals infected with other strains.
9.Guinea pigs and rabbits vary in their susceptibility to the Texas spirochete.
10.Persistence of the virus in the brain of rats over long periods of time was not observed.
11.The Texas spirochete does not penetrate the unbroken skin of young white rats.
12.Young rats may become infected by eating material heavily contaminated with virulent spirochetes.
13.In three “strains” of spirochetes from different sources in Texas identical in cytolytic tests, one failed to cross immunize with the other two.
14.White rats are immune at least ten months after infection.
15.Active immunity in rats may be produced by intraperitoneal inoculations of heat killed spirochetes.
16.Hereditary immunity was not observed in a small number of rats.
17.Passive immunity may be conferred by inoculations of hyperimmune sera.