rRANSFERRENCE OF INFECTION. 503 



matter whether they consist of pus, tubercle or cancer, 

 new young zones are being constantly added on to the 

 old ones, and we may, it we intend to trace the course 

 of development, calculate with great certainty upon 

 always finding the young parts at the extreme circum- 

 ference, the old ones always in the centre. But the 

 zone produced at the latest period of the disease extends to 

 a considerable distance beyond, the zone of degeneration 

 that can be discerned by the naked eye. If we examine 

 any proliferating tumour of a cellular character, we 

 often find, three to five lines beyond its apparent limits, 

 the tissues already in a state of disease, and exhibiting 

 the first traces of a new zone. This is the chief source 

 of local recurrence after extirpation, for it proceeds 

 from the zone that cannot be detected by the naked eye, 

 beginning to grow in consequence of the increased sup- 

 ply of nutritive material which results from the removal 

 of the original tumour. No new deposit from the blood 

 takes place there, but the new-formed germs, which 

 already lie in the neighbouring tissue, run through their 

 further development in the same manner that it would 

 otherwise have taken place, or perhaps even still more 

 quickly. 



This fact I regard as extremely important, because it 

 shows us that all these formations have essentially a 

 contagious character. As long as it was imagined that 

 the mass once formed increased only by the growth of 

 its constituents, it would of course look as if all one had 

 to do for the purpose of getting rid of it was merely to 

 cut off from the tumour all further supply of material. 

 But there is manifestly a contagious matter formed in 

 the tumour itself, and when the cells, which are in its 

 immediate neighbourhood and are connected by anasto- 

 moses with the diseased cells, likewise enter upon the 

 heterologous proliferation, it is impossible, I think, to 



