50 Causes of Disease. 



complicated by other factors, as from the entrance of microbic 

 or toxic agencies through the opening or breach made by the 

 foreign body, with the result of further alteration of the tissues. 

 The traumatic agent may be at the same time the conveyor of 

 such substances, or may itself be a living parasite. Intense 

 mechanical force may sometimes without any evident lesion, 

 sometimes with manifest lesion, cause serioivs and perhaps fatal 

 effects upon the nervous system. For example, this occurs in vio- 

 lent concussion of the body {commotio from com-rnoveo) , espe- 

 cially if the vertebral column be directly affected (concussion of 

 brain and spinal cord — the former causing the loss of conscious- 

 ness, the latter bilateral palsies of the extremities, the bladder 

 and rectum). What the precise anatomical changes are which 

 in such instances take place in the central nervous system has as 

 yet not been determined, autopsy usually showing nothing that 

 is characteristic. Possibly the alterations are molecular. 



Death sometimes takes place suddenly, too, from blows upon 

 the abdominal wall and viscera. Such instances are characterized 

 by sudden loss of strength, fall in body temperature, cardiac fail- 

 ure and diminution of nervous excitability. This condition is 

 known as shock, traumatic stupor, collapse, traumatic reflex par- 

 alysis. It is thought that the paralysis and cardiac failure in 

 such cases is due to vagus irritation. 



Chemical Agents; Poisons. 



Substances which harm the animal body by their chemical ac- 

 tion are known as poisons; the actual process of introduction of 

 the poison and its action, as poisoning or intoxication. Probablv 

 nearly all chemical substances can, under proper conditions, act 

 as poisons, or, in other words, have a deleterious influence upon 

 the tissues ; the mode and power of combination of the chemical 

 and the amount and degree of concentration in which it is present 

 in the body being important items. For example, a substance 

 as essential for the bod\^ as sodium chloride will in large doses 

 cause vomiting and fatal poisoning in dogs. The most poisonous 

 substances, as hydrocyanic acid or nicotine, have absolutely no 

 eft'ect when given in the minute doses of the homeopaths. 

 Changes in the relation of the atoms and solubility may 

 transform a non-poisonous substance into a poisonous one and 

 vice versa; of the two forms of phosphorus, only the white is 



