At any rate this infection of man seems to be the contamination method, the material from faeces and coxal glands being rubbed into the wound made by the tick-bite. The ticks hide in the cracks about the old native huts and bite the sleeping inmates. There may be quite a local reaction at the site of the bite. _Spironema duttoni_ has been cultured by Noguchi, by utilizing his methods for culturing the organism of syphilis. In such cultures he has noted longitudinal division rather than transverse, this fact rather favoring a protozoal as against a bacterial nature. This spirochaete is from 24-30 microns long, about 0.45 micron broad and has a corkscrew motility. It is readily transmissible to a number of laboratory animals, as monkeys, white rats, etc. The spirochaete of Northern African relapsing fever, _S. berbera_, causes the disease as seen in North Africa and Egypt. It is transmitted by lice, Nicolle and others having shown that the spirochaetes make their way from the alimentary tract to the body cavity of the louse. They have shown that the bite alone of an infected louse is innocuous and also that the faeces are non-infective, when injected into monkeys. Emulsions of infected lice, however, when rubbed into wounds, produce the disease in monkeys. _Transmission by the Louse._—The spirochaetes taken in by a louse disappear in a few hours and the insect remains harmless until about the fifth day, when it becomes infectious, and so remains until the twelfth to fifteenth day. Spirochaetes reappear in the coelomic fluid of the louse about the sixth day and continue present until about the twentieth day. A striking fact is that infection can be brought about a day before spirochaetes appear and that after a period of a few days these spirochaete-containing lice lose their power to infect. It would seem that the infecting stage was an invisible one. Have we then a symbiosis between a spirochaete and an invisible virus, possibly filterable? Wolbach has shown that certain spirochaetes will pass through a Berkefeld filter as spirochaetes but this would not affect the possibility of the existence of some granule or chlamydozoal stage. It may be that the infecting stage is not an invisible one but a granule one. _Mode of Infection._—It is by crushing the louse, by scratching or otherwise, that the spirochaetes contained in the coelomic fluid reach and penetrate the wound of the bite. This is therefore a contaminative method of infection. Mackie has shown that the Indian relapsing fever, which is caused by _S. carteri_, is probably transmitted by the louse, and it is probable that the conditions under which the infection takes place are similar to those occurring with _S. berbera_ infections. With the European relapsing fever, bedbugs may possibly act as transmitting agents. The probabilities however are that this infection is transmitted by lice alone.