30 GENERAL ACTION OF DRUGS 



with oxygen. Acetanilid^ potassium chlorate and amyl-nitrite destroy the 

 red blood cellsj if absorbed in considerable amount. 



(c) White corpuscles. — It is possible experimentally to arrest puru- 

 lent exudations caused by irritation and inflammation when quinine is 

 introduced into the blood or applied locally to blood vessels. This hap- 

 pens because quinine and all cinchona salts, berberine sulphate and 

 acetanilid — like other poisons to amebae — prevent the ameboid movement 

 or migration (diapedesis) of leukocytes through the vessel walls. lUnfor- 

 tunately it is impossible to give large enough doses in practice to realize 

 such favorable results in inflammatory disorders. An enormous increase 

 of leukocytes (leukocytosis) occurs in acute diseases accompanied by a 

 local exudation process, and also in leukemia, etc. Nucleic acid may 

 induce leukocytosis and may be valuable in bacterial infections. Its thera- 

 peutic value is still doubtful after many years of trial. Arsenic, and 

 in some cases quinine, appear to reduce leukocytosis, and in leukemia seem 

 thus to aid recovery. Drugs altering the consistency of the blood are: 

 calcium chloride and (to a less extent) other calcium salts, gelatin and 

 potassium iodide, which increase the rate and degree of coagulation; 

 cod-liver oil, which augments the solids in the blood; and toxic doses of 

 mercury, which lessen the solids and coagulation and increase the fluidity 

 of the blood. 



11. — Drugs Acting on the Heart 



The following includes the mechanism controlling the heart, which 

 may also be influenced by drugs : 



1. The heart muscle. This contains the sinus node, which is a 

 part of the heart muscle of the right auricle near the superior vena cava, 

 and is called the pacemaker of the heart because the normal rhythmic 

 impulses start here and spread to the auricles and thence through the 

 small muscle called the auriculoventricular bundle, situated in the septum, 

 and by its two branches to both ventricles. This impulse normally causes 

 the auricles to contract and then, a moment later, the ventricles. 



The heart muscle is itself capable of "rhythmically creating a stimu- 

 lus, of responding to a stimulus by contracting, of conveying the stimulus 

 from muscle fibre to muscle fibre, and of maintaining its proper tone." 



To bring the action of the heart into coordination with the needs of 

 the blood vessels a nervous mechanism is essential, as follows : 



2. Inhibitory apparatus, including vagus roots in the medulla, 

 vagus nerves with terminations in ganglia in the heart, and fibres passing 

 from the ganglia to the sinus node and junctional tissue (between the 

 auricles and ventricles) of the auriculoventricular bundle. 



3. The accelerator apparatus consisting of the accelerator or sym- 

 pathetic nerves with centres (presumably) in the medulla, and in the 

 inferior cornua of the anterior part of the spinal cord, with fibres con- 

 necting with the sympathetic thoracic ganglia whose. cells send fibrils to 

 the sinus node of the right auricle. 



The essential object of the circulation, in the last analysis, is to pro- 

 duce an adequate flow in the capillaries. This depends upon the heart's 

 output, the arterial resistance, and the amount and viscosity of the blood. 



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