EK. V. MeCollum and N. Simmonds 59 
certain within 24 hours, and which have been permanently cured 
‘on the addition to the food mixture of a very smal] amount of a 
preparation obtained in efforts to isolate the unidentified food 
factor, furnish absolute proof that the physiologically active 
dietary factor is being dealt with. Sustained normal function is 
indispensable to adequate proof that the dietary essential in 
question is being administered. If this condition should be in- 
sisted upon by investigators before concluding that a test is 
positive, it is probable that we should not have such a list of 
totally unrelated chemical substances reported as_ protective 
against polyneuritis. | 
Method of Experimentation. 
When young rats are placed upon a diet which is satisfactory 
in every respect except for the absence of either of the dietary 
factors, fat-soluble A or water-soluble B, a considerable gain in 
weight may take place during the first 8 weeks. This does not 
always happen, but with vigorous rats it is of frequent occur- 
rence. After the 2nd or 38rd week, on the experimental diet, 
there is no further increase in weight and either a brief period of 
maintenance is followed by rapid decline or steady loss of weight 
begins and death follows after a variable period, unless the miss- 
ing dietary essential is supplied. Loss of hair and feebleness are 
seen with either type of deficient diet. 
When the diet is lacking in the water-soluble B, but is properly 
constituted in other respects, typical polyneuritis results in many 
of the experimental animals. Funk (7) holds the view that 
beri-beri has not been produced in animals other than man and 
birds, and he believes that only those species whose end-product 
of purine metabolism is uric acid can develop the disease. The 
rat in common with other mammals with the exception of man, 
the higher apes, and the curious exception of the Dalmatian 
)dog recently observed by Benedict (14), excretes allantoin, and 
according to Funk’s classification should not suffer from this 
disease. In our experience rats restricted to a diet which is in 
every way adequate except for the absence of the antineuritic 
substance, water-soluble B, suffer decline in weight and loss of 
muscular control, especially in the hind limbs, and die within a 
few hours unless the necessary complex is supplied. Histological 
