General Etiology of the Diseases of the Peripheral Nerves. 715 



Neuritis. Recent investigations have furnished evidence 

 that neuritis is by no means an uncommon disease in the do- 

 mesticated animals. The explanation of the scanty records of 

 the occurrence of neuritis in the older literature is that in 

 those times it was the central nervous system that was princi- 

 pally examined in cases in which there were nervous disturb- 

 ances, the peripheral nervous system receiving no attention at 

 all or a mere naked-eye inspection. Consequently, the inflam- 

 matory changes in the nerves which are only recognizable on 

 microscopic examination passed unnoticed. 



There is no doubt that cases occur in which the neuritis is 

 due to chilling, but in what manner the effect is produced is not 

 accurately known. There is but little information as to the 

 alterations that occur in nerves as a result of cold, and it can 

 only be maintained with a certain amount of probability that 

 they are of an inflammatory nature. In the vast majority of 

 cases neuritis is due to an infection. The inflammation in such 

 cases is set up by microorganisms or, as appears to be more 

 commonly the case, by their toxins. At the present time, 

 the causes of dourine, strangles, and influenza are known to 

 be capable of setting up neuritis. The results of more recent 

 investigations have shown that certain poisons may cause neu- 

 ritis, provided the animals survive sufficiently long, as in the 

 case of chronic poisoning, or after recovery from a not very 

 severe poisoning. Thomassen furnished experimental proof 

 that lead possesses the power of causing neuritis in certain 

 nerves. Up to the present no evidence has been adduced with 

 regard to other poisons, but it appears to be probable that the 

 same holds good for mercury and arsenic. Many vegetable 

 poisons of known and unknown composition appear to be cap- 

 able of setting up neuritis. Satisfactory and conclusive experi- 

 ments and observations have been made regarding the neuritis 

 caused by polished rice. Mechanical influences (stretching, 

 blows, pressure, etc.) set up chronic inflammation in the con- 

 nective tissue of nerve trunks, especially if they are slight and 

 are in action for a long time, or affect one nerve repeatedly. 

 Finally, some cases may result from the extension of inflam- 

 matory processes that are going on in the neighborhood of the 

 nerve, for example, pleurisy may involve the recurrent nerve, 

 the glosso-pharyngeal nerve, may be affected in pharyngitis or 

 disease of the pharyngeal organs, and severe inflammation of the 

 lymphatic glands may involve any nerve that is near. 



Lesions that are visible to the naked eye are found in only 

 a small proportion of cases, and then only in cases in which the 

 inflammation has led to the production of a large amount of 

 connective tissue, pronounced degeneration, or atrophy. The 

 gelatinous appearance of the perineural connective tissue in 

 animals that are greatly emaciated must not be considered as 

 an inflammatory condition, since the gelatinous infiltration is 



