The main point determined by modern investiga-tion into the action of silver compounds is their special effect upon the nervous system. The best experiments have been made upon animals by hypodermic injection of hyposulphites and albuminates of silver, which do not coagulate albumen. Charcot and Ball reported, as usual results of such injection, paraplegia and paresis of pulmonary nerves, probably reflex in character, leading to profuse bronchial secretion and asphyxia (Gazette Med., 1864). Rouget found that in mammalia, small doses caused excitement somewhat like strychnia; toxic doses induced convulsion and asphyxia. Batrachians got convulsions or tetanic spasm with suspension of voluntary movement, of reflex action, and of respiration, while circulation continued; weakness, torpor, somnolence, and paralysis also occurred in various degrees (Archives de Physiol., 1873). Professor Curci, experimenting on animals with hypodermic injections of hyposulphite of silver, reports that at first they stimulate sensory nerves, and through them the posterior columns of the spinal cord, so that sensibility to impressions and reflex excitability are increased - this condition extends more or less to the motor nerve-tracts, muscular irritability is heightened, and tetanus may be produced: afterward follows a secondary effect of paresis of sensory nerve-centres, and of those connected with respiration; ultimately reflex action is arrested, and respiration and circulation cease. We may accept these facts without assenting to the conclusions drawn by Professor Curci from them, viz., that since silver compounds ultimately paralyze, they cannot be of service in paralysis, myelitis, etc., but are only indicated in spasmodic disorders, especially such as affect respiration (Medical Record, 1877).

Bogolowsky, in his experiments, sometimes found the spinal cord so far affected that the bladder became greatly distended.

An exceptional illustration of the nerve-effects of the drug on man, may be found in the case of a man accustomed for twelve months to dye his hair and beard with a strong solution, and who suffered general weakness, confusion of thought, loss of memory, tinnitus aurium, and defective sight, which symptoms ceased soon after stopping the dye (Bresgen: Schmidt's Jahrbucher, 1874, Bd. clxii.). Within my own experience I have known men suffering from the same cause, with giddiness, vertigo, and marked nerve-depression, amounting almost to melancholia, and recovering quickly after ceasing the application. Convulsions occur in children after toxic doses of the nitrate, but they are probably reflex - i.e., dependent upon gastric irritation (British Medical Journal, i., 1871).

Circulatory System

After intravenous injections of silver salts, the blood has been found dark, pitchy, impaired as to coagulating power, and containing small crystals, and "whitish granulations," which were supposed to be chloride of silver (Rabuteau), but are more probably haematin and protein (Rouget). Ecchymoses have occurred, and, together with the asphyxia and increased bronchial secretion, have been attributed to the altered chemical condition of blood (Krahmer, Monograph, 1845), but such alteration is not produced (in acute form) by silver administered in any other way than by direct injection into the blood. Even toxic doses given in other ways do not alter that fluid beyond some lessened coloration of the corpuscles and increase of fibrin (Bogolowsky, loc. cit., Rouget); the spectrum remains normal. But after the continuous use of full doses of albuminate or phosphate of silver, the blood-condition certainly becomes impaired; the fluid is found to be thinner and darker, and it tends to stagnate in, and transude through, the vessels, while the corpuscles part with haemo-globulin, and become pale, transparent, and angular or oval, with projections: according to Bogolowsky, they do not contain silver, as sometimes asserted.

Sudden arrest of the heart's action, as well as asphyxia with profuse bronchial secretion, were symptoms noted by Charcot and Ball after injections of silver nitrate into the veins of animals. Rabuteau, arguing from the same results, considered the drug to be a "cardiac poison," but it is clear that when thus injected directly into the circulation, the production of thrombosis or embolism may complicate and obscure the special effects of any substance. Rouget found that after hypodermic injection of toxic doses in the lower animals, the heart continued beating after respiration had ceased - i.e., it was not "poisoned;" nor is there any clinical evidence of the salt depressing the circulation, unless in a secondary manner during irritant or chronic poisoning.