14.0 DEPRESSANTS TO CENTRAL NERVOUS SYSTEM 



and depression which is not equally marked, however, throughout 

 the divisions of the central axis. Cushny says concerning this, 

 " The depression seems to be produced mainly in the brain, espe- 

 cially in those parts associated with the higher intellectual faculties, 

 while the stimulation affects first the spinal cord. It seems likely 

 that in different animals these two opposing influences prevail to 

 varying extents, so that in some the stimulant action extends to 

 the brain, as in the cat, while in man the depressant action domi- 

 nates the whole central nervous system, at any rate when moderate 

 quantities are used. The action on the brain is elicited by smaller 

 quantities than that on the cord, so that the first effect of morphine 

 is intellectual depression, while the increased activity of the spinal 

 functions is only elicited by very large quantities. The selective 

 action of morphine is especially evident in the medulla oblongata, 

 in which certain centers are entirely paralyzed before neighboring 

 ones undergo any distinct modification." 



The action of morphine has been studied almost entirely upon 

 the frog and in this animal the reflexes are first diminished and 

 then heightened as in case of strychnine poisoning. This action 

 is seen to some extent in young animals (increased reflexes) but 

 tetanic convulsions are not seen in mammals. There is no good 

 theory to explain the action of the drug upon the different animals. 

 Small doses usually cause drowsiness in horses but larger ones are 

 liable to cause excitement. Opium and morphine are among the 

 most powerfvil and reliable analgesics in man but cannot be de- 

 pended upon for this action in the lower animals, with the exception 

 of the dog. 



To sum up the action oh the nervous system we would say that 

 morphine depresses all the nerve cells in the brain, and very slightly 

 the motor cells. In the cord there is at first a similar depression 

 which may be followed by some hyper-excitability, as shown by 

 twitching, tremors, etc. 



Peripheral Nerves. Morphine has no effect upon either the 

 motor or sensory nerve endings so that its local use is irrational. 

 It is frequently used to check cough and accomplishes this action 

 by reducing reflex irritation or depression of the respiratory center. 



Secretions. The secretory glands, in general, appear to be 

 less active under the influence of morphine. If nausea is caused, 

 there is an increase in the secretion of saliva and mucus but this 

 is due to the nausea and not to any direct influence upon the glands 

 themselves. The sweat glands are exceptions to this general state- 

 ment, for slight diaphoresis is usually seen from therapeutic doses. 

 There is no influence upon the urine. 



Respiratory System. In most animals the respirations are 

 depressed by therapeutic doses, due to depression of the respiratory 

 center, but in the dog there may be panting in the early stages. 



