424 VEDDER AND CLARK. 



In a series of experiments lasting for several years and 

 reported elsewhere, (5) (6) (7) (8) we have had an excellent oppor- 

 tunity to study polyneuritis gallinarum and therefore believe 

 that our observations on its symptomatology and pathology may 

 be of value. In addition, we have made observations which 

 throw an entirely new light on the pathology of this interesting 

 disease. 



I. OBSERVATIONS ON SYMPTOMATOLOGY. 



Incubation pe7iod. — Observers agree that, when fowls are fed 

 exclusively on polished rice, the symptoms of polyneuritis appear 

 in from twenty to thirty days. We have a record of 124 fowls 

 in which the conditions of the experiment were such as to permit 

 an accurate observation of the period of incubation. The average 

 incubation period of the disease in these fowls was 26.86 days. 

 The shortest incubation period observed was seventeen days, but 

 a number of cases occurred in eighteen and nineteen days. On 

 the other hand, in a number of cases the disease only appeared 

 after forty days. These fowls were all fed on polished rice. 

 However, if fowls are fed on a diet of polished rice, but receive 

 in addition small amounts of other foodstuffs, or an amount of 

 extract of rice polishings which is insufficient to afford complete 

 protection, they suffer from the disease in its typical form, but 

 only after a greatly prolonged incubation period. Thus, some 

 of our fowls on such a diet have developed neuritis after ninety 

 days' feeding, and Eijkman records a case where neuritis ap- 

 peared only after a year's feeding. 



Percentage of foivls affected. — Of 211 fowls on an exclusive 

 diet of polished rice, 154, or 73 per cent, have developed poly- 

 neuritis while 57, or 27 per cent, have not shown any symptoms 

 of the disease. The experiments from which this observation is 

 made continued for only sixty days. It is, of course, probable 

 that a higher percentage of fowls would have succumbed if the 

 experiments had been extended over a longer period. 



Course of the disease. — A typical case of the disease may be 

 described as follows. Careful observation during the incubation 

 period will reveal nothing abnormal, except that the fowl may 

 be noticed standing bunched up with ruffled feathers and the 

 comb may become blue. The first symptom noticed is a weakness 

 of the legs, so that the fowl is unable to walk well, and as he 

 steps there is a tendency for the joint formed by the tibio-tarsus 

 and the tarso-metatarsus to give way, causing the fowl to sink 

 to the ground. This is due to beginning paralysis of the extensor 

 muscles of the leg which, it will be remembered, are the first 



