INFECTIOUS DISEASES OF CATTLE. 



369 



animals may disseminate the contagion for a long time without being 

 suspected, and for that reason are the most dangerous of all. 



A more severe type of the plague is the most frequently seen. In 

 these cases the cough is frequent, more or less painful, the back 

 somewhat arched, and the milk secretion diminished. The promi- 

 nence of these symptoms increases, the appetite is affected, the animal 

 loses flesh, the breathing becomes more rapid, the cough more painful, 

 pressure of the fingers between the ribs shows tenderness, the hair 

 loses its gloss and stands erect, the skin becomes adherent, little if 

 any milk is secreted, and the temperature rises, varying in different 

 animals from 103° to 107° F. Animals thus affected may continue to 

 grow worse and die in from three to eight weeks, or they may after a 

 time begin to improve and make an apparent recovery. The inflam- 

 mation of the lung does not, as a rule, subside and the organ return 

 to its normal condition as is the case in ordinary pneumonia, but with 

 this disease the life of the affected portion of the lung is destroyed, 

 the tissue dies and a fibrous wall is formed around it to shut it away 

 from the livingiparts of the body. The tissue, thus encysted, gradu- 

 ally softens, becomes disintegrated and breaks down into pus: The 

 recovery, therefore, is not complete; it is only apparent and partial. 



To those accustomed to examining the lungs of cattle, other and 

 extremely important symptoms may be apparent during the course of 

 the disease. By applying the ear over the walls of the chest an area 

 of a certain extent may be found where the natural breathing sound 

 is diminished or entirely lost. This represents the diseased portion 

 of the lungs. In other cases a loud blowing sound may be heard, 

 quite different from any sound produced when the lung is in a healthy 

 condition. In some cases crepitation is heard near the border line of 

 the diseased area, and friction sounds produced by the roughened 

 pleura; but these can only be appreciated by those whose ears have 

 been trained to distinguish between the different sounds which reach 

 the ear when applied to the chest wall. By percussion — that is, by 

 pressing the fingers of the left hand firmly against the wall of the 

 chest and tapping upon the middle finger with the ends of the fingers 

 of the right hand — an area of dullness may be discovered correspond- 

 ing to the portion where the respiratory murmur has disappeared. 

 This loss of respiration detected by auscultation, and the dullness 

 brought out by percussion, are the most important evidences of an 

 inflamed or consolidated lung. 



Seriously affected animals remain standing if they have sufficient 

 strength, but those which lie down always lie on the affected side. 



The proportion of animals which become affected after being 

 exposed varies accoz-ding to the virulence of the outbreak, the sus- 

 ceptibility of the animals, and the length of time during which expos- 

 ure is continued. Sometimes not over 15, 20, or 30 per cent will 

 61386—08 24 



