A change in latitude has a decided effect, the Northern horse suffering much more frequently than the one which is native to the Southern States and which has inherited the habit of heat endurance.
Finally faults in feeding and above all watering are appreciable factors. The privation of water in particular is to be dreaded. Tracy in his experience with American soldiers in Arizona, found that the command could usually be guarded against sun-stroke when a supply of water was kept on hand. It should be used guardedly, but nothing would act better in obviating an attack. On the other hand, when the canteens were empty, under the hot sun the seizures increased disastrously.
Sheep are especially liable to suffer from heat by reason of their dense fleece, which hinders the evaporation of perspiration, and the cooling effect of air on the skin. When the temperature rises, respiration is accelerated and panting, the lungs seeking to supplement the work of the skin. When traveling in a heavy fleece, or in the hot sunshine in July or August sun-stroke is not uncommon among them.
Lesions. Among the lesions may be named, vacuity of the left ventricle and fullness of the right ventricle and veins with fluid blood or a diffluent clot; congestion of the pia or dura mater, effusion into the ventricles, hæmorrhages into the subserous tissues, and degeneration of the muscles.
Symptoms. Horse. When premonitory symptoms are observed the animal fails to respond to whip or voice, lessens his pace, stubs with his fore feet and sways with the hind, depresses his head and hangs heavily on the bit.
Too often these are omitted or overlooked, and the horse suddenly stops, props himself on his four limbs, drops and extends the head, breathes with great rapidity, panting and even stertor, dilates the nostrils widely, retracts the angle of the mouth and even gapes, has the eyes fixed, the pupils dilated and the beats of the heart tumultuous. The superficial veins are distended, the visible mucosæ congested with dark blood, and blood may escape from the nose. Perspiration usually sets in.
The animal may fall and die in a few minutes in convulsions, or, if stopped sufficiently early and suitably treated, he may in a measure recover in 15 to 20 minutes.
Symptoms. Ox. The premonitory symptoms are like those in the horse: dullness, rapid, panting breathing, the mouth is opened and the pendent tongue is covered with frothy saliva, a frothy mucus escapes from the nose, the eyes are congested and fixed, the pupils dilated, the nostrils and flanks work laboriously, the heart palpitates, the animal sways or staggers and falls. Death follows in convulsions, or it may be delayed, the animal struggling ineffectually to rise, or having periods of comparative quiet. The rectal temperature is very high, 107° to 114° F. If able to stand, there is usually blindness and heedlessness of surrounding objects.
Symptoms. Sheep. The open mouth, protruding tongue, frothy saliva, reddened fixed eyes, rapid breathing, beating flanks, stertor, and unsteady gait are characteristic when taken along with the manifest causes. Swaying movements followed by a sudden fall and death in convulsions form the usual termination of the disease.
Symptoms. Dog. These have been mainly produced experimentally and consisted in hyperthermia, dullness, prostration, accelerated breathing and heart action, congested veins, and mucosæ, muscular weakness, convulsions, and syncope or asphyxia. After death the muscles became speedily rigid, and the blood accummulated in the venous system, was fluid or only loosely coagulated. In these animals, if the experiment were stopped in time the animal could be restored to health.