140 ENTOZOA FOUND IN MAN, 



There will be reason for the belief that a tumour 

 is formed by hydatids when it has produced neither 

 pain, nor fever, nor constitutional disturbance, 

 although it has existed for a long time, and has been 

 slowly developed until it has attained to a consider- 

 able bulk. It should also be borne in mind that the 

 hydatid tumour is usually globular, smooth, and 

 elastic ; that it yields a dull sound upon percussion, 

 and that fluctuation may often be perceived in it. 

 Sometimes, too, it is the seat of a peculiar trembling 

 sensation, which may be regarded as pathognomonic 

 of hydatids. 



When the hand is applied to a cyst containing 

 acephalocysts, in such a manner as to hold it as firmly 

 as possible, a trembling motion, analogous to that 

 which is felt in any vibrating body, will be perceived 

 if a sharp blow be given to the tumour with the 

 other hand. If the tumour be situated where auscul- 

 tation can be employed as well as percussion, a 

 vibratory sound may be heard. 



This phenomenon is not present in all cases of 

 hydatid tumours, and its intensity varies according to 

 the nature of the individual case. The observations 

 of M. Brian9on, who was the first to call attention to 

 it, show that it is necessary that only a small 

 quantity of fluid should be contained in the cyst, in 

 order that the vibrations should be produced,^ 



It has been stated by some writers that the 

 hydatid trembling is not present when the tumour 

 contains only a single hydatid, but this opinion has 

 been proved to be erroneous ; it would probably 



^ " Essai sur le Diagnostic et le Traitement des Aceplialo- 

 cystes," Paris, 1828. 



