INTEODUCTION 15 



tion of free acid from an irritant salt takes place, the 

 modern standpoint of physiology enables one to conceive of 

 the mechanism of its action. Brought into a normally 

 alkaline medium, the acid stimulates the cells to increased 

 alkali secretion in order to counteract the acidity. Similar 

 considerations hold for the introduction of alkali into a 

 normally acid medium. This requires increased circulation 

 of blood and increased cell activity, and whilst tonic when 

 small quantities of acid are concerned, the effect becomes 

 toxic with larger quantities. 



Distribution and Accumulation. — It may now be re- 

 garded as fully established that all poisons, save those 

 which act by the formation of gross lesions resultant 

 upon the destruction of the cells (strong acids and alkalis), 

 causing death by shock, exercise their effects only after 

 entrance into the general, and in particular the arterial, 

 circulation. In a few cases, such as those of arsenic and 

 hydrocyanic acid, these poisons may actually be detected in 

 the blood after administration. The fact that most poisons 

 cannot so be detected is merely due to the lack of sufficiently 

 refined chemical methods of separation and recognition. 

 Thus, atropine produces its remote mydriatic effect, though 

 it could not be chemically detected in the blood or nervous 

 tissue. For this reason a characteristic physiological effect 

 often constitutes a better test than a chemical reaction. 



Before the poison absorbed by the above-mentioned 

 channels can reach the capillary system and cells of the 

 body it must traverse the liver and lungs, which thus play 

 a protective role. Sulphuretted hydrogen may be intro- 

 duced by the rectum, in doses considerably greater than 

 those which prove fatal on respiration. After such ad- 

 ministration the blood, arriving at the pulmonary mucosa, 

 and carrying the dissolved gas, abandons it to the exhaled 

 air, in which it may be detected by the smell, and by 

 blackening a paper soaked in lead acetate solution. 



The liver arrests most metals, phosphorus, and many 

 alkaloids, so that on arriving thereat in the portal system, 

 after absorption from the alimentary tract, the whole or a 



