ACTION OF THE NITRITES 293 



pressure is raised by the nitrites, despite the vascular dila- 

 tation. There is no more quickly acting heart stimulant 

 than nitroglycerin. 



Nervous System. — The nitrites depress, especially, the 

 spinal motor centres, and, in a less degree, the activity of 

 the motor nerves. Reflex excitability is thus lessened. 



Muscles. — Amyl nitrite paralyses muscular tissue when 

 applied locally ; and the nitrites, when administered inter- 

 nally, relieve spasm of muscular tissue by their depressing 

 action upon the motor nerves and muscles. 



Kidneys. — The nitrites augment the amount of urine by 

 dilating the afferent branches of the renal arteries which 

 supply the glomeruli, and so increase the tension within 

 them. The other functions of the body are not affected in 

 any degree by medicinal doses. 



Blood. — In poisoning by the nitrites, the oxidizing power 

 of the blood is lost. Both the venous and arterial blood 

 become of a chocolate hue from the conversion of the normal 

 oxy-haemoglobin into meth-hsemoglobin. The latter yields 

 up oxygen very sparingly. 



Respiration. — The respiratory movements may be 

 increased both in force and frequency by medicinal doses 

 of nitrites, but paralysis of the respiratory centre and 

 asphyxia occurs in fatal poisoning. 



Summary. — The nitrites dilate arterioles, stimulate the 

 heart, depress the spinal motor area, and lessen reflex action. 

 *They relieve spasm and increase the secretion of urine. 



Poisoning. — Fatal poisoning is extremely rare as an 

 accidental occurence. Recovery from a quantity 120 times 

 greater than the normal dose of nitroglycerin, has been 

 reported in human practice. The physiological effects of 

 the nitrites are more noticeable in man, owing to his bare 

 skin. Immediately following the inhalation of amyl nitrite, 

 the face becomes extremely flushed, and throbbing of the 

 vessels of the head, with a feeling of tremendous pressure 

 and headache, ensue. These symptoms are due to vascular 

 dilatation. There is dizziness, the heart is rapid and violent, 



