412 THE BIOCHEMISTRY OF B VITAMINS 



In areas where pellagra is endemic, dogs frequently develop a canine 

 counterpart of the disease known as "blacktongue." In general the symp- 

 toms follow closely those found in humans. The mouth is typically dark 

 red due to necrosis, which in turn causes a drooling appearance and a 

 fetid odor. There is a generalized gastrointestinal disturbance, and the 

 scrotal lesions seen in human pellagra are generally found in black- 

 tongue in dogs. A macrocytic anemia is frequently found, 96 and almost 

 invariably nervous degeneration occurs. The same disease has been pro- 

 duced in dogs in experimental studies by the use of niacin-deficient diets. 

 Because rats do not readily develop a niacin deficiency, dogs have 

 been of great value in the experimental study of niacin deficiency. Recent 

 work has indicated, however, that the frequent anemia seen in dogs with 

 blacktongue may primarily be a simultaneous folic acid deficiency. 97, 98 

 That the etiology of pellagra and blacktongue is not fully understood is 

 readily apparent from the fact that the injection of saline alone is fre- 

 quently curative for blacktongue. 99 In any case it is apparent that many 

 of the symptoms of blacktongue induced in dogs on certain diets are 

 those of folic acid deficiency, and that this condition in the dog is 

 frequently more similar to sprue than pellagra, the balance of the symp- 

 toms in blacktongue depending largely on the diet by which the deficiency 

 is induced. 100 



Pig pellagra also occurs naturally, although with much less frequency, 

 and pigs have been used somewhat in the study of niacin deficiency 101 

 because of the possibility of producing this condition experimentally. In 

 this case there is no glossitis or stomatitis ; the symptoms involve anorexia, 

 slowed growth, a scurfy skin, colitis, and a diarrhea which is generally 

 followed within a month by death. The condition responds promptly to 

 50 mg/day of niacin. Monkeys fed on a niacin-deficient diet similarly 

 become ill and develop anorexia, diarrhea, and dermatitis, and are cured 

 by doses of 5 to 25 mg of niacin. As previously mentioned, rats do not 

 normally develop a niacin deficiency on niacin deficient diets, nor do 

 lambs. 



Biochemical changes in niacin deficiency are not well studied. A change 

 in the urine that frequently occurs in pellagra and has been used in 

 laboratory diagnosis involves an increase in pigments which have been 

 variously identified as coproporphyria I and III or urorosein and indi- 

 rubin. 102 It is generally presumed that these pigments are formed as a 

 result of impaired liver function, and may be responsible when deposited 

 in the skin for the characteristic photosensitive effects in pellagra. It 

 seems well established now, however, that this diagnostic criterion is of 

 little or no value, since a similar result occurs in a number of unrelated 

 conditions, and since many pellagrins do not give a positive reaction. 103 



