HYDATID TUMOURS. 141 



never be observed after the tumoiir has become 

 atheromatous. 



When this phenomenon does exist, it decides the 

 nature of the tumour, but we must be careful not to 

 confound with it the crepitation which is sometimes 

 produced in synovial biu^sse, and in non-inflamma- 

 tory abscesses which are subdivided by small par- 

 titions. 



As a general rule, the absence of pain and of 

 fever will prevent a hydatid tumour from being mis- 

 taken for an abscess, the absence of pulsation, and its 

 slow development wiR distinguish it from an aneurism ; 

 and the absence of pain and of grave constitutional 

 disturbance will suffice to estabhsh a diagnosis 

 between it and a cancerous tumour. 



The diagnosis becomes more difficult when inflam- 

 mation or suppuration have attacked the parts sur- 

 rounding the cyst, as the pain, rigors, and fever 

 might then induce the belief that it was an abscess, 

 and the great disturbance of the system might cause 

 it to be mistaken for a cancerous tumour ; but the 

 previous liistory of the case, and the fact of the 

 tumour having reached a large size before the inva- 

 sion of the fever and of the emaciation, which bears 

 no resemblance to the cancerous cachexia, would 

 throw some hght upon the diagnosis, which the 

 hydatid trembling, if present, would render complete. 



The physical signs of hydatids, such as tumefac- 

 tion, dulness on percussion, fluctuation, and the 

 peculiar trembling cannot, in general, be perceived 

 when the cyst is deeply situated in the chest or in 

 the pelvis ; and the diagnosis is usually impossible 

 when the hydatid cyst is contained within the cavity 



