ORIGIN OF MULTIPLE ECHINOCOCCI. 635 



capsules do sometimes change into hydatids. Of course there is the 

 further difficulty that one must suppose that the primary Echinococcus 

 has first opened into a vessel, and liberated its brood-capsules or its 

 heads into the blood, which then transports them hither and thither. 

 The possibility of this would admit of experimental verification. I 

 regret that I have found no opportunity for so doing, and that the 

 more since I do not share Neisser's a priori objections to this mode of 

 explanation, although I am but little inclined to lay much stress on it. 1 



It seems to me most probable that the multiple Echinococci, or at 

 least the great majority of them, are the result of a single infection, 

 but of one which furnished not one but many embryos. The above- 

 mentioned differences in size and development are easily explained by 

 remembering that the embryos are exposed to diverse external con- 

 ditions, so that some grow more quickly, and to a larger size than 

 others. This idea is confirmed by experience. In examining the 

 animals upon which I had experimented, I have often found consider- 

 able differences in the size and development of bladders, which 

 originated from the same feeding. If such differences be noticeable 

 in worms only a few weeks old, how much greater must they be in 

 the course of a life of years or perhaps decades. 



Probably it is . not only multiple Echinococci which owe their 

 origin to an invasion of numerous embryos. Among the cases of 

 solitary Echinococci it may be that many originated from a more or 

 less abundant infection. We know, too, that it is not exclusively the 

 number of imported germs which determines the issue of a helmin- 

 thological experiment, but also the sum total of the circumstances 

 under which the introduction and development of the young brood 

 occurs. Most emphatic, perhaps, is the fact that the Ccenurus, which 

 is generally found solitary, is not always so from the first. "We may 

 therefore with some probability suppose that the solitary Echinococcus 

 often acquires that characteristic by a sort of selection. There are at 

 first, perhaps, a large number of young Echinococci, of which one (or a 

 few) gradually predominates over, and finally suppresses, the others. 

 When we consider that the disease usually calls for attention only 

 after persisting many years, we can understand why but few of these 

 degenerated Echinococci have been found. I may take this opportunity 

 of recalling the fact that in certain organs the Echinococci are found 

 associated in large numbers much more frequently than in others. 



1 I must leave it undecided whether Morin (loc. cit., p. 34) is right in claiming an 

 embolic origin for the small Echinococci found by him in the lung of a patient infested 

 with a multilocular Echinococcus. He leaves the nature of the embolism undiscussed, but 

 it appears as though he were thinking more of daughter -bladders than of heads or brood- 

 capsules. 



