DISEASES 01? THE CIliCULATORY SYSTEM. 79 



a small hole is, as a rule, to be seen, perhaps several, 

 communicating with the cavity of the tumour, and through 

 this the purulent egg-laden fluid can be easily expressed ; 

 sometimes, and by no means rarely, part of the mature 

 filaria protrudes through this hole and hangs loose in the 

 channel. I have found, connected with the oesophagus, 

 mature tumours embedded, as I have just described, in 

 the muscular walls, similar tumours cretified and enclosing 

 fragments of a long dead filaria, small pedunculated tu- 

 mours of filarian origin projecting into the channel, and 

 long tunnels burrowing between the coats, in some part 

 of which a parasite can be found. In addition to these, 

 the more frequent situations, the animal may be found in 

 large or small glandular-looking lumps in the areolar 

 tissue of the posterior mediastinum, or encysted between 

 the costal and pulmonary pleura. In all these situations 

 I have found them, and also in the same dog. When 

 small, the parasite is found alone, closely invested by the 

 peculiar tissue it seems to create around itself, lying as 

 it were in a tunnel ; but when mature it is found loose in 

 a large tumour, in company with one or more (eighteen I 

 found in one instance), all encapsuled in a common and 

 perhaps cretified cyst, and floating in a purulent fluid." 

 Dr. Manson surmises that the embryo when swallowed 

 attaches itself to the oesophagus, pierces the walls of this 

 tube, remaining in them and becoming encysted, or pene- 

 trating farther to the thoracic aorta. Small worms are 

 most often found in this latter situation, in which pro- 

 bably they do not generally attain maturity, deserting it 

 for the more favorable situation in the oesophagus. Imma- 

 ture worms are single and lie closely invested in their 

 tunnels ; the mature are always in company, sometimes in 

 considerable numbers, and float loose in a fluid enclosed 

 in a cyst. From this it is inferred that when the worm be- 

 comes sexually mature it migrates in search of one of the 

 opposite sex. There are such points of difference between 

 the two blood-worms of the dog as prove that they are 

 not members of the same species in different stages of 

 development, as their frequent occurrence in the same 



