EXPERIMENTAL METAPLASIA 



363 



implanted. Thus it certainly occurred earlier when large cysts, 

 measuring about 4 mm. in diameter, were produced by cutting 

 the muscle and inserting large pieces of the ovary, than when a 

 transplanting needle was used. 



In the course of time, lateral walls dividing the cells appear, 

 and these are usually clearly visible about 40 days after the im- 

 plantation. Thus eventually there is formed a closed cyst, the 

 wall of which is lined with typical columnar ciliated epithelium 

 and surrounds a mass of orange-colored granular debris, in which 

 are numerous blood corpuscles in varying stages of degeneration 

 (figs. 7 and 8). This cyst remains unaltered for at least 120 days, 

 which is the longest period during which I have succeeded in keep- 

 ing the animals alive under experimental conditions. 



So far the sequence of events after implantation of pieces of the 

 ovary producing subsequent cyst formation have been described, 

 it will now be necessary to enter into the modifications of this 

 process that occur when cyst formation does not take place. 



If extremely small pieces of the ovary are im.planted, or if, as 

 sometimes happened in the experiments, the ovarian tissue was 

 distributed thinly all along the track of the needle, cyst formation 

 around the whole implanted mass does not occur. In such cases 

 there is at first a very slight formation of a surrounding layer of 

 agglutinated blood corpuscles, but beyond this, if the experiment 

 has been carried out aseptically, there is very little reaction of the 

 tissues to the implantation in the first few days. The impla^ited 

 tissue often appears quite normal for as long as a week, or eight 

 days, but after this, degenerative changes set in, and by the thir- 

 teenth day at latest, all trace of life in the cells of the oviduct, 

 germinal epithelium, or ova has vanished. Meanwhile the de- 

 generating tissue is invaded by blood corpuscles and fibroblasts. 

 The latter tend especially to invade and travel along any remain- 

 ing framework of connective tissue that may be left in the 

 implanted mass, and thus to form a dense mass of new fibrous 

 tissue in the place of the old. From the examination of a large num- 

 ber of sections of different stages of this process I am of the opin 

 ion that all implanted fibroblasts die, and that all the new fibrous 

 tissue is derived from the cells of the host, though the matter 

 would be extremely difficult to prove definitely. 



