6 BULLETIN 260, U. S. DEPARTMENT OF AGRICULTURE. 
hydatid disease, depending on the location of the parasite. The 
effects are very serious and the prognosis is always grave. A con- 
servative estimate gives a death rate of 13.6 per cent of the persons 
infected (Vegas and Cranwell). The growth of the bladder gives 
rise to various troubles as a result of pressure, obstruction, perfora- 
tion of important organs, necrosis of tissue, liberation of poisonous 
products, secondary bacterial infections, rupture of the hydatid, and 
secondary hydatid infestation following rupture of the cyst. It is 
commonly necessary to resort to surgical interference for the re- 
moval of the hydatid. Operation is often very difficult and may 
have to be repeated, owing to the presence of small external daughter 
bladders which are easily overlooked or incapable of detection. A 
Fig. 2. — Portion of a hog's liver infested with hydatid bladderworm {Ecliinococcus 
granulosus). Natural size (after Stiles). 
case has been recently recorded where the patient had to be operated 
on four times before the recurrence due to daughter bladders had 
ceased. 
In the lower animals hydatids are probably less often a cause of 
death, owing to the slow growth of the parasite and the fact that 
the affected animals are likely to be slaughtered before sufficient time 
has elapsed for the parasite to become a menace to the life of the 
animal. 
If brood capsules containing the tapeworm heads are eaten by 
dogs — a thing which is apt to occur on farms where the viscera of 
slaughtered animals, especially when they appear unwholesome, as 
they would in hydatid disease, are thrown out on the fields or fed to 
