144 \ETERIXAR\' I'ATIIOLOGY. 



they will acknowledge that heat produces all the symptomatic 

 evidences of inflammation and there is no infection. The prin- 

 ciple object in the use of the thermo-cautery is to produce or 

 establish inflammation. A thermo-cautery, or any severe burn, 

 produces tissue necrosis, as well as the destruction of bacteria 

 in that area (sterilization), and an inffammatory zone is im- 

 mediately established around the necrotic tissue which is sterile 

 and may remain free from infection. 



A short exposure to an extremely low temperature produces 

 an inilammatiun. If the exposure is of long duration necrosis 

 is likely to occur. "Chilblains" is an inflammation resulting 

 from temp(jrarv exposure to a low temperature. Sloughing 

 following- freezing of calves' ears, pigs' tails and cocks' combs 

 are familiar examples of necrosis resulting from long exposure 

 to extremely low temperature. An inflammatory zone is es- 

 tablished around necrotic areas produced by freezing similar 

 to the inflanuuatory zone obser\-e(l around necrotic areas pro- 

 duced by burning. Thermic \'ariations may produce chemic 

 substances in injured tissues which are sufflcientl}' irritating to 

 establish inflammation. 



Electric. — It is common knowledge that electricity causes 

 inflammation. Animals injured l)y lightning usuall_y show evi- 

 dences of cutaneous inflammation. In cities animals as well as 

 men frequenth- contact wires charged with powerful electric 

 currents and receive local injuries that are usualU- inflammatory 

 in their nature. 



Chemic. — There arc ma''i}' chemicals that are irritants. A 

 number of them are used as therapeutic agents when irritants 

 are indicated. Mineral acids, caustic alkalies, mercury salts 

 and arsenic are some examples of chemic agents that jiroduce 

 inflammation when applied in dilute solutions, and necrosis 

 when applied in more concentrated form. A 10 per cent solu- 

 tion of nitric acid applied to the skin for a yer"\' short time pro- 

 duces inflammation Inflammatory symptr)ms following the 

 nitric acid application appear immediately; and, as the acid is 

 a disinfectant, the inflammation cannot be the result of infec- 

 tifin. In animals poisoned bv any of the mineral poisons there 

 may always be observed an inflammation in the mucosa of the 

 alimentary tract more extensive than could have been produced 

 by infection in the limited time of action. 



Many reptiles, bees, wasps, and ants introduce chemic sub- 

 stances into animal tissues that are extremely injurious and es- 

 tablish inflammation of very rapid evolution. 



IxiF.rTTOus OR viT,\L .\GENCiES are the most important etiologic 



