3G8 ENZOOTIC AND EPIZOOTIC DISEASES. 



other cause tlie friction sound ; 2d. Tliat engorgement of the lang 

 tissue has taken place ; and 2>cl. That the pericardial secretion 

 is arrected, causing the " to-and-fro " sound at the heart. 



2. In the course of from one to two days the above abnormal 

 sounds disappear. Auscultation now reveals that in the part 

 affected there is no sound at all, or that a tubular or hollow 

 sound is heard. The absence of sound indicates either that the 

 lung tissue has become impervious to air, or that a considerable 

 effusion of serum has occurred into the thoracic cavity. If the 

 former, the absence of sound becomes apparent by degrees only ; 

 that is to say, the respiratory sounds become gradually feeble as 

 the consolidated part is approached, showing that at the border 

 of the hepatized tissue the inflammatory process is less advanced. 

 There may be crepitations or tubal sounds, but when the absence 

 of sound is due to effusion of serum (hydrothorax) the sounds 

 terminate abruptly at a certain distance from the floor of the 

 tliorax, the respiratory sounds being louder than natural above 

 the line of termination, and in some instances the presence of 

 fluid in the chest will be indicated by a " dripping sound," as of 

 drops of water falling into a well. The tubal sounds indicate 

 a less degree of consolidation ; that air finds ingress into some of 

 the bronchial tubes, but not into the more minute ones and 

 air cells. 



This condition may exist for three or more days, and then the 

 crepitations reappear, showing that the exudate is breaking up 

 and becoming gradually removed by absorption ; the dull im- 

 pervious part at the floor of the cavity becoming daily shallower, 

 and the normal sounds slowly returning. 



Percussion during the stages of consolidation and effusion 

 produces a dull sound over the diseased part, and increased 

 resonance over the healthy parts of the chest. In all the 

 unaffected portions of the lungs the respiratory murmur is 

 increased. 



Tlie " to-and-fro" cardiac friction sound also disappears, owing 

 to effusion into the pericardial sac, and reappears as the exudate 

 is removed by absorption. 



Very often after convalescence has been established the cough 

 becomes more frequent; it, however, loses its painful hacking 

 character, being now louder and stronger. In some instances, 

 more especially if the exudate has been very abundant, a mal- 



