44 VETERINARY PATHOLOGY. 



when the lights are allowed to shine directly into their eyes. 

 Epilepsy has been prodnced in horses by sudden exposure to 

 intense light. 



The immediate cause of the effects of exposure to sunlight 

 upon the skin is not known but is thought to be the result of 

 the actiun of the actinic or chemic rays. The effects of expos- 

 ure to light upon the eyes is excessive stimulation which pro- 

 duces exhaustion thus predisposing to, if not directly exciting 

 disease. 



•J. Electric. — Animals are susceptible to the action of elec- 

 tricit\ . Horses are especially susceptible to its influences, a 

 direct current of .")()() volts, IDH amperes, is sufficient to kill a 

 hur>e, and an alternatuig current of KiO volts is destructive to 

 medium sized dogs. 



Contact with electricity may be the result of lightning, and 

 charged electric wires, or rails. Horses and cattle frequently are 

 struck In- ligiitning while in pastures, and animals used in cities 

 arc occasionally accidentally brought in contact with electric 

 currents. Depending upon the amount of electrical current, the 

 results may be a slight singeing of hair, burning, or laceration 

 of tissues in general. Carcasses of animals destroj'ed by electri- 

 cal currents ha\'e also been observed in which no lesions could 

 be found On examination of carcasses of animals dead of 

 lightning strijke, there is usually more or less singeing of the 

 hair, hyperemia and hemorrhages along the course of the cur- 

 rent. 



Chciiiic. — Chemic substances capable of producing disease arc 

 \erv common and may have their origin from the mineral, A'Cg- 

 etaljle or animal kingdom, and are inorganic or organic. It is 

 probable that practicall}- all chemic sul.)stances may, under cer- 

 tain conditions, be injurious to the tissues of the various animals. 

 Some chemicals are alwa_\s injurious, others may become in- 

 jurious ]:)v chemic change induced by the tissue juices. Those 

 chemicals capable of producing deleterious effects in the animal 

 tissues are poisons. (Poisons are substances which when taken 

 internally or applied externally alter health or destroy life with- 

 out acting mechanically or reproducing themselves.) 



.\ccording to their modes of action, poisons have been classi- 

 fied as follows: 1. Corrosive poisons, (caustics and irritants.) 



The action of tliis group varies from the production of a 

 simnle hy|)eremia to necrosis. The most common agents are 

 mercury, arsenic, sodium and potassium hydroxide and the min- 

 eral acids. 



2. Parenchymatous poisons. This ffrouD oroduc^s tJssue 



