8 VETEEINARY TOXICOLOGY 



2. The channel of absorption or administration is of 

 great practical importance in determining the effects of 

 a poison. The channels are — (a) By the respiratory 

 membranes, (b) by the skin, (c) by the alimentary tract, 

 (d) by subcutaneous or intravenous injection. 



(a) The very extensive highly vascular pulmonary mucus 

 offers an excellent channel of absorption not only for gases, 

 of which it is the natural medium, but also of liquids. 

 Large quantities of water are speedily absorbed after in- 

 jection into the trachea, and intrathoracic injection is the 

 most rapid method of giving hydrocyanic acid. The vapours 

 of anaesthetics, of alcohol, and of turpentine, rapidly display 

 their effects on inhalation. 



All soluble poisons are quickly absorbed in this way, and 

 even fats in small quantities. 



(6) The intact skin in general is not a good channel of 

 absorption, but the conditions under which absorption may 

 occur are of extreme importance on account of the frequent 

 application to the skin of poisonous materials, in mange 

 dressings, dips, and the like. Gases are certainly slowly 

 absorbed, but any such absorption has little significance 

 in toxicology. 



Water, and saline solutions, such as solutions of potas- 

 sium iodide, potassium ferrocyanide, and strychnine 

 sulphate, are gradually absorbed, but prolonged contact 

 is required, and the method has no practical importance in 

 toxicology. 



Powders are not easily absorbed, and not at all unless 

 they are soluble in the cutaneous secretions. The skin 

 has a naturally oily secretion, the sebaceous glands are 

 open to the surface, and therefore substances in ointments 

 of animal or vegetable fat are fairly easily absorbed, as, 

 for example, mercury, iodides, and alkaloids. But mineral 

 oil, such as vaseline, does not promote absorption, and a 

 remote action, due to a drug in vaseline excipient, need not 

 be seriously feared. 



In conformity with the fatty nature of the normal secre- 

 tion of the skin, it follows that media capable of dissolving 



