14 MATERIA MEDIC A. 



to act as a laxative in the same manner ; and metallic mercury has 

 been employed to overcome introsusception of the bowels, by virtue 

 of its gravity. 



As regards the absorjotion of medicines into the blood, there is 

 abundant proof of the fact, since they have been detected, after being 

 swallowed, in the different secretions, in the solid tissues of the body, 

 and in the blood itself. Thus rhubarb *and turpentine have been 

 found in the urine ; garlic in the exhalation from the lungs ; sulphur 

 and mercury in the perspiration; garlic, various purgatives, narcotics, 

 and other remedies in the milk; and so on. 



As regards the method by which medicines gain admission into 

 the blood, there can be but two avenues — the lacteals or absorbents, 

 and the veins. From various experiments made upon the lacteals, 

 it is highly probable that their chief, if not exclusive function, is to 

 take up alimentary substances — such as can be converted into chyle: 

 medicinal substances were very seldom found in them. On the other 

 hand, experiments are equally strong in proving, that the veins are 

 chiefly concerned in the absorption of medicinal substances ; thus 

 Magendie found that if the lacteals be tied, nux vomica will affect an 

 animal in six minutes, while, if the veins be tied, no effect is pro- 

 duced. The mode by which absorption is effected is probably, to a 

 great extent, physical, or by endosmose. The rapidity of absorp- 

 tion is influenced by a variety of circumstances, as the part or tissue 

 to which the medicine is applied, the nature of the medicine itself, 

 the condition of the system, &c. It is said to be the greatest from 

 the bronchial mucous membrane. 



There are various circumstances which modify the action of me- 

 dicines upon the system ; these may depend upon the medicine itself, 

 as respects its dose, mode of combination, &c.; or upon the condi- 

 tion of the organism at the time of its administration. Under the 

 latter head, the most important circumstances are: — 



1. Age. — The young are much more susceptible to the action of 

 medicines than the middle aged. Old persons are less able to bear an 

 overdose than middle-aged. It is difficult to lay down any precise 

 rule upon the subject : that of Dr. Young is often adopted ; it is " to 

 diminish the dose of most medicines, for children under 12 years, in 

 the proportion of the age to the age increas'^d by 12 ;" thus at 2 years 



it would be2^2=T' ^^- ^^ *^^' ^^^ ^"'^ ^^^® ^^7 ^® given. There 

 are certain medicines, however, which cannot be given to young 

 children according to the above rule ; thus calomel and castor oil 

 require to be given in larger proportionate doses ; whilst the nar- 

 cotics, and some of the metallic preparations, must be administered 

 in much smaller proportionate quantities. 



2. Sex. — Females, as a general rule, require smaller doses than 

 males. The peculiarities of their system, at the different periods of 

 menstruation, pregnancy and lactation, must also be borne in mind. 



