TRENCH FEVER 699 



healthy lice — that is, the virus is not normally resident in the 

 insect. Further, the infective agent is not transmitted from 

 infected lice to their offspring. The comparative regularity 

 with which the disease may be produced in men of various ages 

 by infected lice, shows that the proportion of naturally immune 

 individuals is very small. 



The American Committee were able in a considerable number 

 of cases to produce infection by simply transferring to healthy 

 individuals lice which had fed on trench fever patients some 

 time previously, the period of incubation being fourteen to 

 thirty-eight days. And in five experiments where means were 

 taken to exclude any other method of infection than the direct 

 bite of the insects, positive results were obtained in all, after a 

 corresponding period of incubation. On the other hand, when 

 infection was by scarification with excrement, they found that, 

 as stated above, the incubation period is much shorter. Their 

 results agree with those mentioned as to a period of several 

 days elapsing before the lice become infective after biting a 

 patient suffering from the disease. 



Both committees confirmed the results of M'Nee and Renshaw 

 as to the transmission of the disease by the injection of the 

 blood of a trench fever patient, the periods of incubation 

 observed also closely corresponding. The American Committee 

 found, however, that the clear citrated plasma is also infective — 

 that is, apparently the parasite is not intra-corpuscular. They 

 attribute the positive results obtained with washed corpuscles 

 to the virus being in part carried down by the centrifuge and 

 thus being present between the corpuscles. They also found 

 that the virus is present in the urine of trench fever patients, 

 and sometimes in the sputum mixed with saliva ; on the other 

 hand, they were unable to detect it in the fseces. Another 

 important result is that on rubbing up the dried urinary sedi- 

 ment in saline and then passing the fluid through a Chamber- 

 land L filter, they were able to set up trench fever by injection 

 of the filtrate. The organism is thus, at least in one stage, 

 a filter-passer. It is relatively resistant; it is not killed by 

 drying or by exposure to sunlight for some time. It survives 

 an exposure to 60° C. for half an hour, but is killed by a 

 temperature of 70° C. for a like period. 



