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THOMPSON YATES LABORATORIES REPORT 
(Case 7, III). If this should prove to be the sole mode of persistence of the contagium, 
the suggested analogy with malaria ceases so far as we yet know the natural history 
of the latter complaint, it is rather the persistence of the parasitic agent in the 
human host, which is chiefly responsible for the endemicity of the disease, and 
in Texas fever also this seems to be the case. 1 Although in yellow fever the 
contagium may not persist in the circulation, its temporary occurrence in the blood 
of natives and their children may be an important factor. From this point of view 
the occurrence of second attacks or of attacks amongst the natives is of considerable 
importance, or, to put it more precisely, the occurrence of attacks of fever amongst 
these people, which, though due to the yellow fever parasite, does not manifest 
diagnostic symptoms of the fever, which is only to be expected in the presence of a 
comparative degree of specific immunity. 
The following is an instance of an early second attack or remote relapse with 
fatal ending : — A.P.D.S., thirty-three years, taken ill thirty days after arrival at Para; 
when seen on the eight day he was much jaundiced and had a high degree of 
albuminuria; there was vomiting but no fever; the icterus and albuminuria gradually 
diminished, and ten days later he was discharged from the hospital. Six weeks after this 
he was readmitted with two days illness ; he had fever and slow pulse (T. 39 0 , P. 70), 
much albuminuria ; uraemia had already set in, and with constant hiccough he died 
on the fourth day of the new attack ; unfortunately no post-mortem examination could 
be obtained. In both instances the diagnosis of yellow fever seemed indicated. Two 
or three persons whom I have seen have told me that about a month or so after they 
had yellow fever they had a sort of relapse of attack, and it is possible that the 
monthly recurrence of ' malaria,' which is talked of in Para, is of an allied nature. 
For quarantine purposes, I am disposed to think that a period of six or seven weeks 
should have elapsed since an attack of yellow fever before an individual should be 
classed as an ' immune.' 
Again, it reads rather more satisfactorily that a man (Case 3, II) was nine days 
in quarantine, than that another was (Case 7, III) seventy-eight days, which appears 
rather a long time for certain knowledge of all his movements short of absolute 
incarceration. Still, apart from these criticisms, the striking feature of the experiments 
is the statement that amongst the local community only those persons who had been 
subjected to artificial inoculation contracted the disease. 
The first nine experiments (I) were uniformly negative : of these an eight-day 
period in the gnat was the maximum, except in two cases, where it was ten and 
thirteen respectively, but the sources were very mild cases on the fifth day of disease. 
In the latter cases it is shewn that not every gnat which has been fed upon a yellow 
fever case during the first three days of illness is capable of conferring the fever. 
1. Thco. Smith, The Aetiology of Texas Cattle Fever. Ne-w Tot k Medical Journal, July 8, 1899. 
