318 ON GROWTH AND OVERGROWTH 



with, for, accepting the purely histological use of the terms, we 

 can unreservedly agree with Israel that it is a matter of taste 

 whether we speak of a given tumour as an " endothelioma 

 carcinomatosum or sarcoma endotheliale." For routine clinical 

 purposes they are most valuable. When a tumour has assumed 

 a carcinomatous or a sarcomatous appearance it is coincidently 

 locally malignant, if not in all cases generally malignant also. 

 The terms, therefore, have a clinical significance and value. Only, 

 let me repeat, they are valueless for purposes of relationship and 

 classification, and must bear no embryogenetic signification. 



To explain these peculiarities of lepidomatous tumours let 

 me point out that 



1. After the embryonic period, it would seem that hylic 

 tissues never take on lepidic characters. We have no instances, 

 that is, in which, after embryonic life, we recognize that lining 

 membranes or glands become differentiated from connective 

 tissues. 



2. It is generally held that the converse is also true. 1 With 

 regard to tumours we find the same principle evidently in 

 operation. 



3. We may confidently lay down thai all tumours and portions 

 of tumours containing cell layers or cell groups of the lepidic 

 type have been derived from pre-existing lepidic tissue. 

 Possibly this so-called principle is more of the nature of a 

 postulate than of a proved law ; we take it for granted, and 

 may not be able to prove our position in every case. We have, 

 that is, fairly numerous examples of neoplasms of lepidic type 

 developing in situations in which normal lepidic tissue is not 

 present adenomatoid tumours of the bone, gland-like follicles 

 in the midst of uterine fibroids, cysts, or tubular spaces lined by 

 cubical or columnar epithelium in gliomata and the list might 

 be lengthened. 



1 True, that is, until Beard's rather startling observations upon the origin 

 of leucocytes is confirmed. According to this observer the first, and indeed the 

 main, development of leucocytes is to be found as a process of proliferation and 

 metamorphosis of the hypoblastic epithelium of the follicles of the foetal thymus 

 gland. Beard's observations were published eighteen months ago, but to the 

 best of my knowledge they still lack confirmation. Leo Loeb also (Arch. f. 

 Enlwicklungsmech. d. Organ., Leipzig, vi., 1898, and Medicine, April 1899) has 

 thought to see connective tissue cells undergoing origin from the Malpighian 

 layer of the skin : his observations have not gained acceptance. In lower 

 forms of life, however, some definite cases of regeneration of hylic from lepidic 

 tissues have of late been brought forward. 



