These views are that colloidal silica in water is responsible for the disease. Voegtlin noted the great amount of aluminium in certain vegetables and suggested this as the toxic causative substance. A mixture of colloidal alumina and silica in water is supposed to be operative as well as silica alone. Against the colloidal silica hypothesis is the statement of Sandwith that the water of the Nile, the drinking water of Egypt, is low in colloidal silica content.
3. Long has suggested that amoebae may be the cause.
4. Tizzoni has incriminated a streptobacillus which he stated he found in the blood and organs of pellagrins as well as growing on maize.
Epidemiology.—As the result of very careful epidemiological studies the Thompson-McFadden Pellagra Commission came to the conclusion that there was evidence against the transmission of pellagra by ticks, lice, bedbugs, cockroaches, fleas, mosquitoes and buffalo gnats (Simulium).
They were rather disposed to consider that the disease showed a greater prevalence where the disposal of faeces was unhygienic, as in unsanitary privies, and that the existence of an efficient water sewerage system prevented pellagra. If faecal bacteria should act as infectious agents then the house fly would possibly be worthy of suspicion.
Many of the peculiarities of sex and place distribution could be explained by the stable fly, Stomoxys calcitrans, a fly which bites viciously in the district in which they worked. This fly bites only by day and is intimately associated with human dwellings so that the greater incidence of the disease in the women, who stay at home, as against an incidence five times less in the men who work in the mill during the day might be explained by Stomoxys bites.
At the same time their failure to transmit pellagra to monkeys by injections of defibrinated pellagra blood would militate against any infectious agent existing in the blood. It may be stated that Harris has claimed to have produced a disease resembling pellagra in two monkeys by injecting filtrates from emulsions of brain, skin and intestinal tract of cases dying of pellagra.
Lavinder and Francis injected 79 monkeys and 3 baboons with varying material from pellagra autopsies. Some of the animals were injected with emulsions or Berkefeld filtrates of such emulsions made from brain and cord. Other monkeys were inoculated with material from skin similarly prepared, others with stomach and mouth mucosal emulsions, and still others with intestine and faeces emulsions. Blood, urine and cerebro-spinal fluid were also injected. Feeding experiments were also carried out. With one exception, and that one only suggestive of pellagra, the experiments were negative.
Sixteen volunteers, working under Goldberger, tried to infect themselves with blood, nasopharyngeal secretions, epidermal scales, feces and urine from pellagrins. Various atria of infection were tried according to material; blood by intramuscular injection, excreta by mouth. After a period of six months all the subjects of the experiments remained well. This evidence is certainly against the infectious nature of the disease.