502 IXFLUENZA 



milder in form, probably due to a gradual attenuation of the 

 virus. 



The pe^'iod of incubation varies from two to seven days. 

 Siedamgrotzk}^ places it at from four to five days and in rare 

 cases from 12 to 24 hours. In some cases S3'mptoms have not 

 appeared until from two to five weeks after the latest known 

 exposure. 



§ 388. Symptoms. The disease appears suddenly and 

 ma}-- attain its highest point of intensit)^ within twenty-four 

 hours. The organs of circulation, nervous centers, digestive 

 and respirator}' mucous membranes and conjunctiva are 

 especially affected. There is partial or entire loss of appetite 

 and depression. The temperature ri.ses suddenly from 3 to 

 4° F. or even more. It remains high with but slight variations 

 for from three to six days and then falls rather quickly, often 

 within twenty- four hours, to the normal. At first the fre- 

 quency of the pulse is but little increased in comparison to the 

 elevation of the temperature, but later it rises to from 60 to 70 

 and in fatal cases from 80 to 100 or more. It generally con- 

 tinues high for some time even after the temperature has 

 fallen. The fever is characterized by unevenness in distribu- 

 tion of the external temperature of the body. The early rise 

 of temperature, while the affected horses appear to be healthy, 

 is of much diagnostic value. 



Usually the nervous depression coexists with the fever. 

 The animal ma}' hold its head down and appear to be coma- 

 tosed. Extreme muscular debility is frequenth' associated 

 with this stupor. Tremors may occur, the hind legs ma\- give 

 way while walking and paralysis of the hind quarters appears 

 in a few cases. 



The oral mucous membrane is greath' congested, hot, dry 

 or covered with mucus. There is sometimes difficulty in 

 swallowing. The animal frequently yawns. There is usually 

 constipation in the beginning of the disease which ma\' be 

 accompanied with colic. The feces are formed into small hard 

 balls and are covered with masses of mucus. Later diarrhea 



