Etiology. 



755 



nerve that is iirst affected is the vagus and its branches. The 

 sympathetic suffers to a less degree, and in the nerves of the 

 extremities the lesions are very slight and cause no functional 

 disturbance. Vachetta observed polyneuritis in a fowl as a re- 

 sult of lead poisoning, but ]\Iarek was unable to produce the dis- 

 ease by introducing large quantities of lead into the crop. In 

 dourine it is principally the proximal portions of the nerves that 

 are affected, but in lead poisoning it is the distal segments. 



An error will scarcely be made if it be supposed that there are other causes 

 of polyneuritis in the domesticated animals. The nervous symptoms seen in chronic 

 mercury poisoning are probably due in part to a polyneuritis, but the question 



-yO^ 



Fif,^. 114. Cross section of the femoral nerve of a fowl affected with jjolyneuritis. 

 (a) Extensive infiltration of the endoneurium with mono-nuclear cells. (b) Scat- 

 tered i^ersisting nerve fibers, (c) Cross section of blood vessel, (d) Slight cellular 

 infiltration of the perineurium abutting on the epineural tissue. 



whether mercury and other metals and viruses can cause polyneuritis cannot at 

 the present moment be answered with certainty. In a case recorded by Lellmann 

 as ' ' infectious polyneuritis ' ' the symptoms were in all j)robability due to chronic 

 ossifying pachymeningitis of the cord. 



In Batavia, Eykmann observed a disease resembling beri-beri in 

 fowls after feeding with cooked rice. The disease had an incubation 

 period of three to four weeks or more, and on the grounds of histolog- 

 ical examination he stated that it was a polyneuritis. The disease could 

 be produced experimentally in fowls by prolonged feeding with de- 

 corticated rice; birds of prey and apes were refractory. 



