NEURALGIA. 319 



finger by striking the ulnar nerve near the inner condyle of the hu 

 menis, or in the toes by a blow on the sciatic nerve where it escapes 

 from the sciatic notch, is also a genuine, pure neuralgia. Practically 

 it would be better to designate as pure neuralgia those cases that con- 

 tinue after the cause that induced them has ceased to act. Among the 

 injuries that may be regarded as direct causes of neuralgia, the most 

 frequent are : 1. Wounds of the nerves from sharp instruments, such 

 as lancets, needles, etc. ; a complete solution of continuity is far less 

 dangerous than these punctured wounds. 2. Irritation from foreign 

 bodies that have entered and become incapsulated near the nerve ; ob- 

 stinate neuralgia has very often been observed as a result of the irrita- 

 tion caused by pieces of musket-balls. 3. Compression of the nerves 

 by contracted cicatrices. 4. Pressure on the nerves by aneurisms, ex- 

 ostoses from bones and teeth, and tumors, particularly carcinoma. 5. 

 Neuroma, described in the last chapter. 6. Overfilling of the veins in 

 the vicinity of the nerves where they pass through bony canals. From 

 the predisposition of the left side of the body to intercostal neuralgia, 

 Herile concludes that the latter cause has a material influence on the 

 occurrence of neuralgia. The left side differs from the right in the 

 arrangement of the venous circulation, so that the blood must make a 

 circuit (from the hemiazyos vein into the azyos) to pass from the veins 

 of the spinal cord into the vena cava ; if there be any obstacle to the 

 escape of blood from the heart, it must necessarily have a worse effect 

 on the left side than on the right. The theory that neuralgia often 

 depends on dilatation of the venous plexuses surrounding a nerve where 

 it passes through an opening in the bone, is also supported by the fact 

 that the first branch of the trigeminus (whose relation to the venous 

 plexuses in its vicinity resembles that of the intercostal nerves) is far 

 more frequently the seat of neuralgia than the second or third branch, 

 where this is not the case. In the so-called rheumatic neuralgias, 

 caused by catching cold, we can find no material changes in the neu- 

 rilemma to explain the irritation of the nerve ; nevertheless, although 

 hypothetical, it is very probable that this rheumatic neuralgia is due 

 to a hyperaemia and cedematous swelling of the neurilemma, which 

 disappears after death. Lastly, we may mention, as causes of neu- 

 ralgia, poisoning by metallic substances, such as mercury, lead, copper, 

 etc., as well as by malarial infection. It is perfectly inexplicable, in 

 these cases, why the irritation from a constitutional disease should 

 only affect a very circumscribed nerve-tract. 



SYMPTOMS AND COURSE. In neuralgia we may distinguish two 

 forms of pain : one continuous, increased by pressure, confined to cir- 

 cumscribed points in the course of the nerve (points douloureux, Val- 

 kix > 8) 3 not very severe but annoying pain ; the second occurs in parov- 



