Unfortunately the results obtained from the different experiments with corn were not concordant, and further confirmation is necessary before Thomas's figure for the biological value of corn protein can be accepted as final. (See p. 264).

It was after analysis of the pellagrous and non-pellagrous diets from this point of view that Wilson arrived at the conclusion that danger of pellagra occurred if the " biological value" of the protein ration was below a certain level. This level, as might be expected, varied within certain limits according to individual need and idiosyncrasy, hard manual labor needing a more generous provision in this respect. This view is in accord with many of the known facts of the incidence of the disease. For example, upon this theory pellagra would be likely to develop with greatest frequency upon a diet consisting largely of corn, owing to the low "biological value " of the proteins of this cereal; at the same time the disease might occur among wheat and rice eaters, in cases of an exceptionally low total consumption, but it could rarely occur among populations taking meat or milk even in small quantities. The protein deficiency which leads to pellagra, and is possibly concerned with a defective supply of some essential amino-acid or acids may, in Wilson's opinion, occur also upon an adequate diet if assimilation is defective as the result of gastrointestinal disease.

This theory would account for certain rare cases, occurring in England and elsewhere, of a disease with symptoms closely resembling those of pellagra. In these instances there has frequently been a. history of chronic diarrhoea and gastro-intestinal disturbances of long standing.57

54a During a pellagra outbreak in Egypt, Bigland (Lancet 1920, 1, 947) attempted to obtain organisms from the blood and feces on various media, complement fixation with alcoholic extracts of organs obtained at autopsy, inoculation of rabbits with pellagrous sera and the diagnostic use of maise extracts, but failed of positive results. An examination of the diets of these pellagrins showed that there was a deficiency in the "biological value of protein," but there were a few cases in which no such deficiency could be proved. To explain these cases, it is assumed that some toxin is formed which acts upon the intestine or its contents in such a way that protein is not properly assimilated.

55 Wilson, quoted in Rep. 38, Med. Res. Com. London, p. 95, 1919.

56 Unpublished work.

The observations of Chick and Hume on the effect of feeding specific proteins and amino acids to their pellagric monkeys is in accord with this view. The administration of tryptophane to one monkey staved off death for many weeks, while a mixture of lysine, arginine and histidine had little effect. In one case in which there were severe skin lesions the addition of five to 10 g. of casein produced a cure which is described as " dramatic".

While there is a growing tendency to regard pellagra as the result of a deficiency of certain essential amino acids it must be admitted that cases have been reported which are difficult to explain from this point of view. Enright, reporting on the outbreak of pellagra among the German prisoners in Egypt, states that:

"A careful analysis of the diets of these German prisoners before capture and during their period of captivity prior to the onset of the eruption, showed that they were ample, both in quantity and quality, for any possible requirements, and were of such varied composition that it is difficult to see how they could be improved."58 He coneludes, therefore, that food deficiency cannot be regarded as the principal factor. Goldberger58a argues that the evidence offered by En-wright and also by Viswalingam is insufficient, inasmuch as the ration given may not have been consumed in adequate quantity, owing to racial differences in taste. Even more impressive are the cases reported by Silcr, Garrison, and McNeal,59 of pellagra appearing in tubercular patients who were on the rich diet of milk and eggs prescribed for that disease. On the other hand, as Hess has pointed out,60 while adequate protein, milk, cheese, eggs, and meat, were all lacking to a pronounced degree in the Central Empires during the war, there was no marked prevalence of pellagra during these years.

57 See also McCollum and Simmonds, J. Biol. Chem. 32, 250; 33, 303,1917; Rpof, Roy. Soc. Med. Sec. Ther. Pharm. Nov. 1919, Lane. 1919, ii, 979.

58 Enright, Lancet, 1920, i, 998. See also Viswalingam, J. Trop. Med. 23, 40, 1920.

It is obvious that more extensive investigations must still be made before we can entirely reconcile the conflicting evidence recorded. Bory61 regards pellagra as a disease which can develop only under the conditions brought about by a one-sided diet, usually exclusively cereal, but believes that the infection is actually transmitted by some winged insect. This theory is supported by two cases recently encountered in France, one an Italian soldier who developed the disease in France after coming from a hot-bed of pellagra, and the other a sporadic case developing in a region in northern France where no other instance has been known before or since. A body of Italian troops had been camped in the vicinity for several weeks, and Bory believes that the mosquitoes which infested the district had become infected and carried the disease. The one man contracting it was predisposed, as he had lived for years on an exclusive diet of milk, rice, and other cereals on account of chronic digestive disturbance.

58a Goldberger, Lane. 1020, II, 41.

59 Third Rep. Thompson Pell. Com. p. 113.

60 Hess and Unger, J. Am. Med. Aas. 74, 217,1920.

61 Bory, Prog. Med. 35, 461, 1920.