FOOT-AND-MOUTH DISEASE 379 



One attack produces immunity for only a short period 

 (usually not over one year). In certain individuals no 

 immunity is conferred, the animal suffering within a few 

 months repeated attacks. Calves born of cows attacked in 

 advanced pregnancy are sometimes (not always) highly 

 resistant to either natm-al infection or artificial inoculation. 



Symptoms. — The period of incubation is two to seven days, 

 although it may be longer. 



The prodromal symptoms are those of fever, the tempera- 

 ture reaching 106° ¥., lasting one or two days, and falling to 

 normal as soon as the vesicles appear. Unless complications 

 arise from secondary infection, no further rise in temperature 

 occm-s during the course of the disease. 



With the fever there is a period of loss of appetite, sup- 

 pressed rumination and languor. The mouths of the patients 

 become sore, causing them to masticate slowly and in an 

 interrupted fashion. The mouth is usually held closed, saliva 

 hanging from the commissures in long strands. When opened 

 a peculiar smacking sound is made. - Where a number of 

 affected cattle are housed together the noise produced is 

 marked. 



On examining the mouth one to two days after the begin- 

 ning of the attack, the mucous membrane, especially of the 

 lips, gums, dental pad and tongue, shows a vesicular eruption, 

 the individual vesicles varying in size from a pea to a walnut. 

 The large blisters rupture in about one day, leaving behind an 

 excoriated surface of a brown-red color, which is often covered 

 with a gray deposit. The smaller vesicles persist for two to 

 three days. On the back of the tongue one to three walnut- 

 sized vesicles are often noted. As the organ is extremely sore 

 and therefore little moved, the blisters remain intact for two 

 to three days. The contents of the vesicles are clear or 

 yellowish. Where they erupt a very sensitive, highly red- 

 dened, shallow erosion is left which becomes covered with new 

 epithelium in two to three daj's. When healing is well under 

 way the eroded area appears as a brown-yellow spot which 

 eventually disappears. As soon as the erosions are sufficiently 

 covered with epithelium, the emaciated patient begins to eat. 



In some cases the muzzle (^out of swine), base of the 



Digitized by Microsoft® 



