216 



A DICTIONARY. 



impression, which they produce on the parts 

 with which they are first brought in contact, 

 is transmitted along the nerves to other 

 parts. The latter mode of operation is 

 sometimes called action by sympathy. 



(a.) The great majority of medicines ap- 

 pear to act in the former of these two ways, 

 being taken up by the blood-vessels from 

 the sm-face of the mucous membranes, sldn, 

 or other part to which they have been ap- 

 plied. Thus, most medicines given by the 

 mouth, after having, if solid, undergone 

 solution in the acid gastric juice or alkaline 

 bile, pass, by a process of endosmose, into 

 the capillary veins which ramify on the sur- 

 face of the stomach and intestines, enter 

 the general circulation by the mesenteric 

 and portal vessels, and are thus carried to 

 all parts of the body, altering, it may be, 

 the nutritive processes of various organs 

 and tissues, and at length expelled through 

 some of the excretory channels, as the skin, 

 kidneys, or bowels. The rapidity with 

 which most substances are thus absorbed, 

 and make the round of the circulation, is 

 almost incredible. Professor Hermg, of the 

 Veterinary College, Stuttgardt, found that 

 yellow prussiate of potash injected into one 

 of the jugular veins of a horse appeared in 

 the other in twenty-five seconds, and was 

 exhaled from the mucous and serous mem- 

 branes in a few minutes.; and also that 

 chloride of barium injected into the jugular 

 vein of a dog reached the carotid artery in 

 seven seconds. Dr. Blake observed that 

 chloride of barium and nitrate of baryies 

 traversed the whole circulation of a dog in 

 nine seconds, and that of a horse in twenty 

 seconds; and a similar rapidity of distri- 

 bution doubtless obtains with substances 

 which cannot easily be detected in the blood. 



(b.) The other hypothesis, regarding the 

 action of medicines, is that they owe the 

 development of their effects to the produc- 

 tion of some nervous impression on the 

 part to which they are first applied, and its 

 subsequent transmission to remote organs 

 by means of the nervous system. A recent 

 modification of this theory, advanced by 

 Messrs. Morgan and Addison, assumes that 



the nervous impression is produced, not 

 upon the part with which the medicine is 

 first brought in contact, but on the interior 

 of the blood-vessels after partial absorption. 

 Part of the evidence in support of these 

 hypotheses is derived from the fact that 

 some poisons operate with such extreme 

 rapidity as to render it- doubtful whether 

 there could be time for their being absorbed 

 and making the round of the circulation. 

 Thus: anhydrous prussic acid, conia the 

 alkaloid of hemlock, and aconita the alka- 

 loid of aconite, when injected into the 

 veins, applied to the cellular tissue, or given 

 by the mouth, produce almost instantaneous 

 effects, and death in a few seconds. It ap- 

 pears, however, that the strongest evidence 

 in favor of the theories under consideration 

 consists in the effects of local injuries in 

 producing constitutional disturbance. For 

 example, a blow on the region of the 

 stomach sometimes causes fatal swooning ; 

 distention of the stomach often produces 

 hiccough ; the presence of worms in the 

 intestines sometimes induces epilepsy ; and 

 a local injury frequently causes fever and 

 constitutional distm-bance of all the more 

 important organs of the body. In such 

 cases the connection between cause and 

 effect obviously depends on the transmis- 

 sion of nervous impressions only. And if 

 topical causes are thus productive of remote 

 effects, it is siu"ely fair to infer that medi- 

 cines and poisons may operate in a similar 

 manner. 



In fine, although it would appear that 

 most medicines are absorbed and actually 

 conveyed to the parts on which they act, 

 and that such absorption and actual con- 

 tact are essential to their action, yet it is 

 highly probable (though not yet positively 

 ascertained) that some substances, espe- 

 cially the more active poisons, astringents, 

 and emetics, owe their effects to the pro- 

 duction of a nervous impression, and its 

 propagation to remote organs. Nor is it at 

 all improbable that, under different modify- 

 ing influences, certain substances will oper- 

 ate sometimes in one and sometimes in 

 the other of these two ways. 



