PRESCRl 19 



frequently of the red or white corpuscles ; that is, 

 have an effect in it, but little or no effect on it. The 

 student must carefully note the fact, that very few 

 medicines produce their characteristic effect by acting 

 upon the blood. 



3. Specific action. Leaving the circulation, drugs 

 enter the tissues and organs, alter the anatomical 

 and physiological state of one or more of them, and 

 are then said to have a specific action upon these. 

 In most instances this is the characteristic and most 

 important part of the action of the drug. 



4. Remote local action. Medicinal substances, 

 having passed through the tissues, are finally cast out 

 of the body by the excreting organs, whether in the 

 same form as they were admitted, or as the products of 

 decomposition in the system. The kidneys are the great 

 channel of escape for drugs; the lungs ("breath"), 

 skin, bowels, mouth, mammary gland, and all mucous 

 surfaces and wounds, to a less extent. Whilst thus 

 passing through the excreting organs, the active prin- 

 ciples of drugs frequently exert a further or remote 

 local effect upon them, not infrequently resembling 

 their immediate local influence. 



Prescribing. When the practitioner desires to 

 employ drugs for the purposes of treatment, he turns 

 to his knowledge of the action and uses of the materia 

 medica, selects his remedies, and proceeds to order one 

 or more of them, according to a recognised form or 

 formula, which is called a prescription. This is a very 

 difficult proceeding when first attempted, being nothing 

 less than a serious and probably sudden practical test 

 of one's acquaintance with an enormous subject. The 

 beginner should know, therefore, what points are spe- 

 cially to be kept before him under these circumstances. 

 Briefly, they may be said to be the following : 



1. Selection of the remedy. This is, of co 

 the first and fundamental proceeding of all. It is 



