Two experiments were performed in which a total of 17 dogs were fed a blacktongue-producing diet and 17 controls were fed the same diet but given adequate supplements of nicotinic acid twice weekly. The dogs, after being on their respective diets for an average of 10.4 weeks, were infected orally with trophozoites of Entamoeba histolytica, given in salol-coated gelatin capsules.
A much greater percentage of the experimental dogs than of the controls was positive for amebae in rectal samples taken ante-mortem (88.2 and 41.1 respectively), and the average prepatent period was considerably shorter in the experimental animals (2.1 and 4.9 days, respectively). At necropsy, performed 3–10 weeks after infection, E. histolytica was demonstrated in 82.4 per cent of the experimental dogs and in 58.8 per cent of the controls. All of the experimental dogs had amebic lesions, with an average number of 31.5 lesions, whereas only 70.6 per cent of the controls had lesions, the average being only 3.8.
Since the experimental dogs and controls were handled similarly, except for supplements of nicotinic acid given to the controls, it would appear that in this host nicotinic acid is involved in the mechanism of the resistance to E. histolytica. Other experimental studies in dogs are cited which seem to have a bearing on this conclusion. In addition, observations of one authority on pellagra suggest that these results might have a similar relationship in man.