1913] Sweet: Epithclioiita of the Common Fowl 37 



Tissue Eeaction. — The tissue changes described by Reischauer 

 (1906), Bvirnet (1906), Apolant (1902), and many others, were 

 noted. These are mainly as follows : There is a marked h.yper- 

 plasia of the epithelium, the number of cells being greatly in- 

 creased, and the individual cells being greatly enlarged. The 

 cells apparently increase in number by the usual method, that 

 is, the cells multiply in the stratum germinativum by mitosis 

 and in the portion.s of the growth removed from the growing 

 layer undergo only secondary changes. It also appears that the 

 growing layer is unequally stimulated, since the proliferating 

 epithelium takes the form of cell nests or buds projecting down- 

 ward into the underlying connective tissue and upward to form 

 the caiiliflower-like growths which appear on the .siarface of the 

 epithelium. These buds or fingers of epithelial cells, on section, 

 very much resemble in appearance a true epithelioma. They are 

 supported by thin strands of connective tissue, there being con- 

 siderable hyperplasia of the underlying connective tissue. In 

 the advanced stages of the disease this hyperplasia of connective 

 tissue elements is much more marked. However, the excess con- 

 nective tissue may in large part be due to the secondary infection 

 which is always present. In addition to the above noted changes 

 there is a marked engorgement of the underlying blood vessels 

 and a considerable wandering of leucocytes into the tissue (in- 

 cluding the epithelium) lying about the vessels. Even, in the 

 early stages, before secondary infection has apparently taken 

 place to any marked degree there is the tissue reaction that is 

 present about a focus of infection. In other words, the nature 

 of the tissue reaction speaks strongly for the infectious nature 

 of the disease, varying from the picture presented by the ordin- 

 ary pyogenic infection only in the unusual reaction of the epith- 

 elium. As has been noted, there is an enormous increase in the 

 number of epithelial cells. Besides this, the individual cells be- 

 come as large as 40 /j. in diameter. The epithelial cells lying 

 next the connective tissue are about normal in size, stain deeply 

 and are undergoing rapid proliferation. Their walls are well 

 defined, the cytoplasm dense and finely granular, and the nuclei 

 are normal in appearance. The cells outside the deepest layers 

 in the epithelial bud become progressively larger, stain less 



