CHAPTER VII. 

 NOTES ON PRESCRIBING. 



As each patient must be considered as an individual and given separate 

 care and thought, it is impossible in such a book as this, which does not 

 treat of therapeutics, to do more than indicate some of the points which 

 must be understood and borne in mind when about to write a prescription. 



Drugs are administered by the physician either for a local effect, that 

 is, produced in the immediate neighborhood of the point of application, 

 or for their remote effect, that is, produced generally on various organs 

 throughout the body, or on some special organ remote from the point of 

 application for which they have a special affinity. 



It is consequently essential for the prescriber to decide in the first 

 place what organs he wishes to influence and whether they are such as he 

 can reach by local application or not. Then in the second place, he must 

 decide what drugs he desires to use to affect these organs. 



For Application to the Skin. Very few drugs can be absorbed into 

 the system through the skin with such rapidity that they accumulate 

 within the body sufficiently to be used by the physician for their remote 

 pharmacological action. The outstanding example of those that do so is 

 mercury. Most other drugs are excreted by the kidney and bowels so 

 much more readily than they are absorbed from the skin that no remote 

 action can be expected. 



The rapidity with which drugs may penetrate the skin can be greatly 

 increased by dissolving them in some solvent which penetrates more 

 readily than they do themselves. Such solvents are used as the bases of 

 those ointments from which we wish a'n action after absorption. Alcohol, 

 to a slight extent, olive-oil, wool-fat, and lard, are all absorbed by the skin. 

 Olive-oil is perhaps the best base to aid absorption. Wool-fat is very 

 nearly as good, while lard is not very efficient. The paraffins, resins, 

 and soaps, are scarcely absorbed at all, and solution in them rather delays 

 than furthers the absorption of substances made into ointments or plasters 

 with them. 



A local effect, but one produced in the skin after absorption, is naturally 

 more easily obtained. Oil of Mustard developed in a mustard poultice or 

 plaster, Cantharidin from its Collodion, Liquor, Emplastrum,Unguentum, 

 or Tincture, Croton Oil, Turpentine, Ammonia and Chloroform, readily 

 pass through the skin and by reflex stimulation set up a more or less marked 

 local inflammation and possibly a remote reflex effect. The student will 

 note that the bases of Unguentum Cantharidis are more soluble in the skin 

 than those of the Emplastrum and consequently contain a lower percen- 

 tage of Cantharis. Atropine, morphine, cocaine, camphor, potassium 



108 



