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Dr. C. Bolton. Physiological Action of a [Mar. 20, 



Heart. — During the first rise of pressure the rate of the heart becomes 

 slower and the individual pulsations larger towards the end. During the 

 slight succeeding fall the rate becomes slower still, the pulsations being 

 larger. As the pressure curve rises the second time the rate becomes rapid, 

 and the pulsations frequently irregular in size. As the pressure finally falls 

 the pulsations becomes smaller, and towards the end too small to count, they 

 are still more rapid and irregular in size and rhythm. 



Respiration. — There is no effect on the respiration until the blood pressure 

 falls towards the end, when it may become shallow. 



As the heart stops, irregular respirations or large inspirations are taken. 

 After the blood pressure has fallen to its lowest limit and there are no cardiac 

 pulsations, inspiratory gasps may be taken at intervals for more than a 

 minute. 



It thus appears that the action of the poison is directed against the 

 circulatory apparatus and that the effects upon the respiration are secondary. 

 There is no evidence that respiration is directly affected ; even when the 

 voluntary muscles are paralysed the animal still breathes and gasps are 

 taken after the heart has stopped. The blood in the left side of the heart 

 which is found dilated is bright red, showing that asphyxia plays no part in 

 bringing about death. 



The rise of blood pressure appears to be chiefly due to vasomotor con- 

 striction, since the heart is slowed. The subsequent rapidity of the heart 

 indicates an increased irritability, the vagus being unable to hold it in check 

 and hence the blood pressure rises, but subsequently falls as the muscular 

 power of the heart fails. 



Effect of Abdominal Compression. 



Even when the blood pressure has almost fallen to its lowest limit the 

 heart is capable of responding to the increased amount of blood supplied to 

 it by abdominal compression and the blood pressure rises, but if the com- 

 pression is persisted in the heart fails and the blood pressure falls in spite of 

 the compression. 



This experiment illustrates the wonderful reserve power the heart possesses 

 even when almost dead and it shows that the final fall of blood pressure is 

 not a pure vaso-motor phenomenon, as in that case the blood pressure would 

 be restored by abdominal compression and the heart would not suddenly fail. 



There is, therefore, a direct action of the poison upon the heart muscle, the 

 heart failure being a primary phenomenon. 



