42 Causes of Disease. 



nution in vascular tone). As anatomical changes are found red- 

 dening of the skin (in hogs), failure of blood coagulation, dilata- 

 tion of the right heart, venous hypersemia of the lungs, liver, 

 kidneys and brain. The names insolation and sunstroke are ap- 

 plied to that form of heat-stroke which is caused by the influence 

 of the direct heat-rays of the sun upon the body, particularly 

 upon the head ; it is thought to depend upon a paralytic dilatation 

 of the vessels of the meninges and cortex of the brain, and the 

 fiffection is accompanied by convulsions and marked symptoms of 

 excitation (Birch-Hirschfeld). 



The influence of heat locally applied occasions, lesions known 

 as hums (combustio), of various grades according to the 

 degree of temperature, the duration of application and the resist- 

 ive powers of the tissues to heat. Burning may result from con- 

 tact with solid, liquid or gaseous heated matter, or from direct 

 action of a flame or radiant heat. Short exposure to a tempera- 

 ture of 40 to 50°, or longer exposure to 30 to 40° C. is pro- 

 ductive of an inflammatory reaction marked merely by dila- 

 tation of the capillaries (hyperemia) and redness of the part 

 {inflammatory hum, erythema, hum of the first degree or of mild 

 degree). The process is only superficial, leading at most to 

 desquamation of the epithelium. Exposure to heat of 60 to 80° 

 C. {hum of the second or intcmiediate degree) is productive, 

 in addition to the hypersemia, of rapid exudation of serous 

 fluid from tha dilated vessels beneath the epithelial layer. The 

 cells of the stratum ]\Ialpighii are pressed apart by this, become 

 swollen, are loosened from the papillary bodies, and the firm, 

 horny portion of the epidermis is raised up to form a blister. 

 Through minute fissures, easily made in this bleb, pyogenic 

 bacteria may enter, the fluid contents through further exuda- 

 tion [leucocytes] becoming turbid and purulent. Should the 

 blister rupture the hypergemic papillje beneath are exposed, the 

 repair of the epidermis starting from the epithelium at the mar- 

 gins of the lesions or from remnants of the ]\'Ialpighian cells 

 which were not destroyed. In case of mucous membranes, which 

 are devoid of the horny epithelial layer, blister formation is not 

 likely to take place, the epithelial layer desquamating in shreds ; 

 and the denuded surface is covered by a coagulating exudate, the 

 so-called croupous or false membrane. The more severe influ- 

 ences of heat, above 80° C. {burns of the third degree), 

 produce searing and charring {eschar formation) ; the burned 



