ACTION OF MEDICINES ON THE EYE 89 



undesirable, on account of their tendency to dissolve the 

 corneal cement. The antiseptics generally used are mercuric 

 chloride and boric acid, the latter frequently conjoined with 

 an equal quantity of sodium sulpho-carbolate. The ano- 

 dynes preferred are atropine, cocaine and eucaine. The 

 sensitiveness of the eye is increased by strychnine. It is 

 diminished, and local anaesthesia produced, by cocaine, 

 which, accordingly, is serviceable in some examinations, as 

 well as in operations on the eyes. The lachrymal secretion 

 is increased by pungent odours from such volatile oils as 

 mustard and onion, and by physostigmine. It is diminished 

 by atropine. 



The pupil is dilated by belladonna, atropine, homatropine, 

 cocaine, daturine, and hyoscyamine. Such dilators are 

 termed mydriatics. The pupil is contracted by calabar 

 bean, eserine, opium, morphine (see opium), pilocarpine, and 

 nicotine. They are termed my o tics. Anaesthetics, and 

 some narcotics in full doses, first contract, and afterwards 

 from circulation of venous blood dilate, the pupil. The 

 action of most mydriatics and myotics is purely local. Most 

 mydriatics are anodynes, and hence are useful to allay irrita- 

 tion, inflammation, and pain. They are used in iritis to 

 prevent adhesions. Dilating the pupil, they facilitate ex- 

 amination of the lens for cataract and of the retina. Myotics 

 are used alternately with mydriatics to discover adhesions of 

 the iris, and to break them down, to restrict the passage x)f 

 light in painful diseases of the eye ; and to lessen intra-ocular 

 tension, as in the earlier stages of glaucoma. 



ACTION OF MEDICINES ON RESPIRATION 

 ERRHINES AND EXPECTORANTS 



Respiration consists in the alternate enlargement and 

 diminution of the cavity of the chest, whereby air is alter- 

 nately inspired and expired. These movements, so essential 

 to the life of all the higher animals, are chiefly presided over 

 by a nerve-centre or group of ganglionic cells, situated in the 

 medulla, posterior to the vaso-motor centre, and extending 

 into the anterior part of the spinal cord. This centre is 



