=8.= =Climate and Season.= This is notoriously an important factor. At Paris, Trasbot met with 237 cases in the nine months from October to June inclusive and but 8 cases in the summer months—July, August and September. In Great Britain, where the vicissitudes are less severe Percivall had in the cavalry horses in the seven months from October to April inclusive 146 cases = 20.85 Per month, and in the 5 months from May to September inclusive 62 cases = 12.4 per month. _Exciting Causes._ Nearly all the above causes when acting with unusual force may become direct factors in causation. The effect of a sudden and extreme chill is especially to be feared. Even in cases that are unquestionably due to a microbe as the essential cause, the nervous disorder manifested in the chill, and the clogging of the pulmonary circulation in connection with the retrocession of blood from the surface of the body furnishes the opportunity for the colonization of the germ. The average horse at pasture will stand with impunity cold storms of rain, snow, and sleet, and transitions from a warm noonday sun to a cold night wind and dew and even frost, but under other conditions of the system, with the fatigue and fret and sudden changes of food and regimen attendant on domestication, or with any derangement of an important bodily function the _chill_ is often the manifest occasion of disturbance of the balance of health, and the supervention of pneumonia. =Fatigue=, a system charged with =leucomanies=, and a =free perspiration=, which is suddenly checked by exposure, at rest, to a =cold rain=, or =snow=, to a =draught between door and window=, to =immersion in the cold waters= of a river, or to =sponging with cold water= is quite liable to cause pneumonia. An unduly heavy winter coat, an individual peculiarity or determined by a cold environment in autumn often predisposes strongly to such dangerous chills, by the frequency and profuseness of the perspirations and general relaxation of the system. Clipping of such subjects is a true hygienic measure though it entails the need of extra care in blanketing. Again in the animal that has already suffered from disease of the respiratory organs these chills are more dangerous factors. =Direct irritation= by inhalation of smoke and other products of combustion; or acrid or irritant gases or dust; by the drawing of food by aspiration into the lungs (as in paralysis of the larnyx or pharnyx, choking, apoplexy, vomiting, etc.); by pouring irritant or insoluble drugs (oil, lard) through the nose; by the pressure of neoplasms (actinomycosis, tubercle, glanders, cancer); or by the presence of parasites (strongylus, distomata, echinococci, linguatulas). _Pneumonia_ from =Contusion= of the chest, fracture of a rib, or puncture or laceration of the lung is recognized.