6 



in man is in correlation to tlie frequency with whicli sheep and 

 oxen suifer from the same disease, and, above all, in correspon- 

 dence with the very common presence of the adult tapeworm 

 in the dogs of Iceland. In Iceland, at the time of Krabbe's 

 report, there were for every 100 inhabitants 488 sheep and 36 

 horned cattle ; pigs, however, were scarce. Now, the propor- 

 tion of sheep and cattle per 100 inhabitants in G-reat Britain, 

 according to Mulhall's balance-sheet of the world, 1870 to 1880, 

 is — sheep 93, cows 29. 8o that if we include under the com- 

 mon title of " domestic herbivora" sheep and horned cattle, we 

 shall see that in Great Britain, per 100 persons, there were of 

 domestic herbivora 122 ; in Iceland, 524. Tersely, then, in 

 Iceland there are per head of human population more than 

 four times as many possible hosts for hydatids as there are in 

 Great Britain. Now, as regards the possible hosts of the 

 tapeworm, i e., the dogs. According to Krabbe there was in 

 Great Britain in 1855 about one dog to every 50 inhabitants. 

 In Iceland, at the time of his investigation, about one dog to 

 every three to five inhabitants, i.e., there were, at his lowest 

 computation, ten times as many dogs per head of population 

 in Iceland as in Great Britain. From this it follows, other 

 things being equal, that an Icelander was threatened with 

 hydatid infection from the dogs ten times more than an Eng- 

 lishman, and, besides that, every Icelandic dog had four times 

 as many chances of eating the host of an hydatid as an English 

 dog. But there are two other very important points to con- 

 sider, viz., the opportunities that the dogs have of eating 

 hydatids, and the chances of a man swallowing the eggs of the 

 tapeworm. Of course the number of domestic herbivora and 

 of dogs form only two elements in the chain of causation of 

 hydatid disease. The most important elements by far are the 

 numbers of these animals infested with the parasite, and the 

 chances of mutual infection of the dogs and domestic herbivora. 

 And, first, how many sheep, for example, are there affected 

 with hydatids in the two countries ? As regards Great Britain 

 I have no data, but as concerns Iceland we have some facts, 

 and in this connection I cannot do better than quote the fol- 

 lowing statement by Dr. J. Hjaltelin, who for many 

 years was the chief medical officer for Iceland. He writes : — 

 " I have for many years been investigating how frequent 

 this disease is in the Icelandic sheep, and I have come 

 to the conclusion that traces of it are found in more than 

 every fifth sheep ; nearly all the peasants have ascertained that 

 this parasite may be found in every third sheep that is more 

 than three years old. In a district called Skaptar-Syssel, with 

 about 3,000 inhabitants and 22,000 sheep, the Echinococci are 

 said to be found in every adult sheep, and it is worth attention 



