the primary circumstance of the triato- 

 ma's being a domestic insect with habi- 

 tat, perhaps confined to human dwelling- 

 places, and preferring to nourish itself 

 on human blood during sleep. Under 

 these circumstances, and to judge by 

 the biology of ])lood-parasites it was 

 to be admitted that the flagellate of the 

 Intestine of the blood-sucker, whose food 

 is chiefly human blood, should undergo 

 a gradual adaptation to the blood-medi- 

 um and, at a given moment of its 

 philogenetic evolution, become a parasite 

 of man. Up to this point I was frankly 

 in the realm of hypotheses, undoubtedly 

 based on exact biological reasons but 

 that nevertheless still awaited con- 

 firmation. Furthermore I was at that 

 time unaware of the important fact that 

 even in uninhabited regions, armadilloes 

 (T'atusia novemcincta) are frequently in- 

 fected v/ith Trypanosoma Cruzi. This 

 observation, completed by the finding 

 of Triatomn genicnlata, infected v> ith try- 

 panosomes in armadillo-holes led me to 

 the conviction, jusiified by vaincus argu- 

 ments that the natural and ancestral 

 host of the parasite is really the arma- 

 dillo and that the himian infection is 

 the result of a later adaptation. 



This point of view hr.rdly to be op- 

 posed, since it has in its favour positive 

 facts of observation as well as undenia- 

 ble biological arguments, would explain 

 the existence of infected triatomala in 

 regions were the disease is unknown. 

 As a matter, of fact, some people, with 

 the curious object of denying Trypanoso- 

 ma Cruzi any pathogenic action, state 

 that the barbeiro has been found in some 

 regions of Brasil and other countries 

 carrying in its digestive tube flagellates 

 that could be inoculated into small labo- 

 ratory animals and that nevertheless the 

 disease had not been reported in these 

 regions. 



Now, in the first instance it would be 

 advisable to relate the clinical and expe- 

 rimental researches proving the inexis- 



teufc of the disease, whose parasitolõ* 

 gicid diagnostic is not an easy matter 

 and as a rule is possible only post-mortem. 

 And as for acute cases, to happen upon 

 them it would be necessary to remain 

 some time in the region. It would be of 

 more use in excluding the existence of 

 trypanosomiasis to carry out minute cli- 

 nical observations based on an exact 

 knowledge of the symptoms that cha- 

 racterise the different forms of the di- 

 sease. Only after this had been done 

 could one claim, that in this or that 

 country, in one or another region, 

 there were triatomata infected with pa- 

 rasites that could be inoculated in small 

 laboratory animals without there having 

 been observed any human infections. 



But granting the opinion of those 

 vsho disbelieve in american trypanoso- 

 miasis, unless we want to deny the exis- 

 tence of the disease altogether, which 

 would be absurd in view of the exact- 

 ness of the clinical observations, the 

 post-mortem findings, and the experi- 

 mental results, demonstrating in full 

 the scientific interest and social impor- 

 tance of the disease, we are obliged to 

 accept the above-mentioned apparently 

 contraditory fact, taken from my con- 

 clusions, namely that in these regions 

 tlie adaptation of the trypanosome to man 

 is not yet accomplished and that the races 

 o!). ser ved in the blood-sucking trans- 

 mitter are not virulent for human be- 

 ings. In any case this is a question in 

 itself, but under no circumstances will 

 it be possible to find bona-fide and logic 

 argimients to displace the evidence of 

 facts acquired by observation and expe- 

 riment. 



It svas along these lines, that I 

 started a new phase of my work by sear- 

 ching for trypanosomes in those patients 

 for whose disease I had foimd no inter- 

 pretation. 



At first all attempts gave constan- 

 tly negative results a fact which was later 

 explained by the absence of parasites 



