This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
Whether the muscles or nerves are primarily affected, and in the latter case whether the peripheral branches or the centres are most at fault, has been much debated. Giacomini attributed the colic to direct muscular irritation from deposition of the metal in the abdominal muscles and the diaphragm, pointing out that superficial pressure often gives pain, even over the iliac crests (where the intestines are not), while firm supporting pressure relieves. Briquet, acting upon this theory, faradized the skin of the abdomen with a metallic brush, and thus relieved the pain by counter-irritation. That the paralysis also depends on deposition of the metal in the muscles is suggested by the frequency with which the right arm is affected in lead-workers, it being more exposed to the poison than the left.
Tanquerel maintained that the colic was due to irritation of the great ganglionic centres, though signs of this could only be found in one out of forty post-mortem examinations. It may be noted, however, that galvanism of the sympathetic nerve-centres has been said to cause elimination of the poison quickly, and to cure palsy of the forearm without direct local treatment (Medical Times, i., 1877).
Eulenburg considers lead colic "a mixed neurosis of motor-sensory nature, in which the splanchnic nerves and vaso-motor branches from the aortic plexus are affected" (Medical Times, i., 1870). He points out the special determination of lead to the muscular system and its powerful local effect in causing contraction of involuntary muscles.
Heubel argues that the peripheral intra-muscular extremities of nerves are at fault rather than main trunks ("Bleivergiftung," Berlin, 1871), and Althaus apparently takes the same view (Medical Times, i., 1874, p. 548). On the other hand, Bernhardt asserts that the real lesion is in the gray matter of the cord (Medical Record, 1878), and most modern observations point to the same conclusion, at least in chronic conditions; lead has been found in its substance in some cases (Chatin, v. p. 251), and a granular partly atrophic state of spinal cells has been verified in one instance by Lancereaux. The affected muscles and corresponding nerve-trunks are much atrophied, so that sometimes scarcely one normal fibre can be found.
Full medicinal doses of the acetate slightly lower the force and frequency of the pulse (Laidlaw). In hemorrhagic cases and in pneumonia this effect is often marked. Strohl found a diminution of ten to fifteen beats per minute after daily doses of 25 to 50 ctgr., and Rabuteau verified a pulse-rate below that of health; it has been explained by a direct action on the muscular structure of the heart. In cases of acute lead-poisoning, the pulse has been sometimes quickened, but has become slow in the stage of collapse. In subacute cases it is markedly slow and feeble. During a paroxysm of colic in the course of plumbism the pulse is of characteristic wiry hardness, and generally lowered in frequency, while the heart-action is so weakened as to be scarcely perceptible. In half the large number of cases recorded by Tanquerel, the pulse-rate was from 30 to 60 per minute, the hardness and slowness being usually proportioned to the amount of pain; exceptionally the frequency was increased. The peripheral circulation is commonly impeded, and arterial anaemia leads to pallor and chilliness, though in two cases recorded by Murchison a rise of temperature (102°) was found (Lancet, i., 1868). In chronic conditions of lead-poisoning the pulse is small, hard, and usually slow, and the sallow, bloodless skin has an icteric tint, anaemia is commonly marked, and there is more than normal water in the blood as well as fewer red globules; Malassez states, however, that these are increased in size (Archives de Physiol., 1874). Cardiac murmurs are usual in lead-workers, and it is said that the heart and great vessels have been found smaller than usual after death. Henle considers that the vessels are contracted (during life) by direct irritation of their muscular coat by lead circulating with the blood; certainly vascular tension is much increased in plumbism, as clearly shown by the sphygmogram of Dr. A. Frank (Deut. Arch. Klin. Med., Bd. xvi., Hft. 3). German observers, besides corroborating this, have demonstrated the antagonistic effect of pilocarpin during attacks of colic; very soon after its hypodermic injection the tracing shows greatly lessened tension, and simultaneously the pain is relieved. Nitrite of amyl acts similarly (Medical Record, 1876).