PREDISPOSING CAUSES 



1717 



it had two seasons, during which it appeared in swarms and at- 

 tacked man and animals — viz., spring and autumn, and not in 

 summer — a fact which we have been able to confirm for one of the 

 regions which we visited. 



The Illinois Commission and many others have been unable to 

 support the relationship of pellagra to Simulium. 



The epidemiological evidence in favour of the spread by a biting 

 fly is, however, very strong. 



Summary. — It appears to us that while at present the causa- 

 tion of pellagra is unknown, and while the modern tendency 

 is to claim it as a deficiency disease, still the investigations 

 of a possible protozoan parasite and its carrier should not be 

 given up. 



Predisposing Causes. — Sex would appear to be a predisposing 

 cause, because the disease is often more prevalent in women than 

 in men, and this would not appear to be so mysterious as it seems 

 at first sight, for if there is anything in Sambon's fly theory, the 

 women ought to be more exposed to the flies than the men, because 

 they wash the clothes in the neighbouring streams. In one place 

 where this incidence was most marked the men worked all day 

 underground in mines, and the women presumably in and about Ihe 

 houses, which were on the banks of a fly-infested stream. Here 

 the children also were much affected. In interesting contra- 

 distinction is the incidence in the women of Burano, who mostly 

 work indoors and among whom pellagra was very rare ; but it was 

 common among the fishermen and boys who fish in the rivers, etc., 

 where biting flies are common. 



Age would not appear to have any marked influence, but it 

 would seem as though the disease was very prevalent — in a mild 

 form, at all events — in the early years of life, as the children of 

 a pellagrous district are often early affected, and some of these 

 attacks are by no means mild, but very severe. 



With regard to social position, poverty, lack of sufficient food, 

 and bad hygienic surroundings, it was long considered that these 

 had a marked influence in producing the disease, but though they 

 may help, as they would, with almost any form of disease, still, 

 the American and our own experience show that they have no real 

 onnection with pellagra, which can equally well occur among the 

 well-to-do, the well-fed,and those living in circumstances of good 

 hygiene, though more commonly met with among the poor and those 

 ill-fed and living in circumstances of bad hygiene. 



There is a definite correlation between the lowering of the general 

 resistance of the body against disease and an acute exacerbation 

 of pellagra. Thus pregnancy, an attack of any illness, but especially 

 enteric fever, may induce either an exacerbation or the first re- 

 membered attack of the disease. 



, Sunlight per se is not a causal factor, as far as we know, in the 

 disease, but it is a powerful predisposing cause in helping to develop 

 the dermatitis. 



