EXPERIMENTAL METAPLASIA 371 



degeneration, are present. These orange granules resemble in 

 appearance the orange colored yolk substance of the ripe ova, 

 and the amount of this granular substance within the cysts seems 

 to be independent of the length of time during which the implanted 

 tissue has been allowed to remain in the muscle. If implantation 

 of pieces of the ovary of approximately equal size have been made, 

 examination of the contents of a cyst after 6 days will show as 

 much of this substance present as in a similar cyst after 120 days, 

 hence it appears that this substance cannot escape through the 

 cyst wall. When it is considered that the development of the 

 ciliated epithelial lining only occurs as a reaction to the implan- 

 tation of ripe ova, containing a plentiful supply of the orange 

 colored yolk substance, there is at least a possibility that the or- 

 ange substance within the cysts bears a close relation to the yolk 

 substance, and that the development of ciliated epithelium from 

 the fibroblasts lining the cyst is a specific reaction to its presence. 

 Though based on no experimetal evidence, I would suggest as 

 a possible explanation of the phenomena, that some substance 

 is formed as a result of the ingestion of these orange granules by 

 the blood corpuscles, and their subsequent degeneration wdthin 

 the cj'st: that the granules themselves remain unchanged, and 

 are again set free on the disintegration of the corpuscles, and that 

 their action on the protoplasm of the corpuscles is merely catalytic. 

 This substance, produced from the blood corpuscles, is probably a 

 fluid, and would be slowly and continuously formed as long as 

 blood corpuscles could pass through the walls of the cyst. The 

 action of this substance on the fibroblasts forming the w^alls of 

 the cyst is to delay their return to the spindle shape typical of 

 the resting condition, and eventually to set up those changes in 

 the inner layer of fibroblasts resulting in their conversation of cili- 

 ated epithelium. Once this epithelial layer is complete, the access of 

 fresh blood corpuscles to the interior of the cyst would be hindered 

 or prevented, and so the formation of this substance would tend 

 to stop; at the same time the outer layers of fibroblasts would 

 regain the resting state, and form a la^^er of typical fibrous tis- 

 sue which would tend still further to prevent the ingress of fresh 

 blood corpuscles. 



