220 ANIMAL PAEASITES. 



the smaller ramifications of the portal vein we may certainly 

 conceive it possible that although the majority (vide supra, 

 in the general section) might migrate actively out of the vessels, 

 yet an embryo might exceptionally become further developed 

 within the interior of the vessel. It is certainly possible, 

 at the same time, that in rare cases only, a subsequent pene- 

 tration of the ready-formed Echinococcus-colouy into the in- 

 terior of the vessels and an advance of them might take place. 

 For wherever an embryo is capable of closing the passage of the 

 vessel, wherever it can resist the force of the current of blood 

 pressing against it in such a way as to be enabled to continue 

 its individual being and life, it will become further developed, 

 although its external appearance during growth must certainly 

 be modified by the local anatomical circumstances. What is 

 described by Buhl, Zeller and others, as alveolar cancer and 

 alveolar colloid, is certainly, as Virchow states, as well as his 

 own case, an Echinococcus of the lymphatic system of the 

 liver. Probably all cases of Echinococci of the liver, of similar 

 anatomical structure, both in man and animals, are also Echino- 

 cocci of the lymphatic system. It is of no consequence to 

 the increasing vesicle, which, as is well known, penetrates 

 into all vacuities in the tissues, so long as it only can find 

 room. 



Thus, then, it forms a larger vesicle in the lymphatic vessels, 

 probably as a sort of centre or colony from which runners 

 penetrate towards all the lateral branches of the lymphatic 

 system ; these go off exactly like the fingers from the palm of a 

 glove, and send off radiating runners in every direction where a 

 lateral branch of the lymphatic system enters. Thus a very 

 great part, nay, perhaps the greatest part, of the lymphatic system 

 of a liver may be penetrated by such runners from one centre, and, 

 strictly speaking, become obsolete. The penetrating branches of 

 the colony, however, will be constantly dilating the lymphatic 

 vessels into which they have penetrated, as they meet with no 

 very great resistance from the soft parenchyma of the liver, and 

 at the same time also thicken their own walls, which, however, 

 also puts an end to the dilatation of the walls of the vessels 

 themselves. Thus, at all events theoretically an Echinococcus- 

 embryo may permeate the whole liver, or at least a very great 

 part of it, if it has penetrated into the lymphatic system. 



But, nevertheless, the walls of the vessels will present obstacles 



