but on fluids secreted by itself from tbe blood of its host. 

 It is extremely important to remember that sbeep and oxen 

 get the hydatid, and the dog the tapeworm. JN'o one has ever 

 seen this rule reversed in the ease of Echinococcus. Man, in 

 his relation to Echinococcus, resembles the sheep and ox, and 

 not the dog, for he gets the hydatid cyst, but not the little 

 tapeworm. The great practical fact is this : — That if there 

 were no dogs we should not get hydatid disease. Eating 

 underdone mutton or beef can never give us hydatids, though 

 it might give us certain kinds of tapeworms. The dog, how- 

 ever, would not get Taenia Echinococcus if it did not swallow 

 living scolices from hydatid cysts. Kow, if all this be correct, 

 we can see that the existence of a great many dogs, sheep, 

 oxen, pigs, &g., in a country produce favourable conditions 

 for the propagation of hydatid disease in man, for the 

 greater the number of dogs the greater the number of 

 hosts for the tapeworm form, and in like manner the greater 

 the number of sheep, &c., the greater the number of hosts for 

 the cystic form. There are four chief factors which determine 

 the spread of hydatid disease in any country : — 1. The num.ber 

 of dogs in the country. 2. The opportunities that exist for 

 enabling the eggs, bred in the dog, to be swallowed by the 

 sheep. 3. The number of sheep, oxen, pigs, &c. 4. The fre- 

 quency with which dogs eat the organs of infected sheep con- 

 taining living hydatids. Take a country with many sheep, the 

 organs of which are often eaten raw by dogs, let the water 

 supply be scanty and procured from bogs, swamps, waterholes, 

 and dams, on the banks of which dogs may deposit the eggs, 

 to be blown in by the winds, and washed in by the rain ; let 

 there be dogs in abundance, and w^e then have all the condi- 

 tions necessary to the spread of the disease. 



The G-eographical Disteibl'tiox of Hydatid Disease. 



This disease is known to occur with greater or less frequency 

 in all countries inhabited by Europeans or their immediate 

 descendants. Prom G-reat Britain to America, from Denmark 

 to Bengal, from Iceland in the north to Xew Zealand in the 

 south, may this ubiquitous parasite be found. It would be safe, 

 I think, to assert that wherever man and his faithful com- 

 panion and servant, the dog, are found together, there will be 

 found, with greater or less frequency, hydatid disease in the 

 former. But the frequency of the disease varies greatly in 

 different countries, and I shall give you as briefly as I can, the 

 facts bearing upon this point, at least as far as I have been 

 able to ascertain them. More particularly, I shall bring 

 before your notice, figures illustrating the frequency of the 



