" MIXED TUMOUES " : EMBRYOMAS 335 



blastemas (or tumours due to the aberrant growth in the organism 

 of one individual of cells and tissues of that individual himself). 

 So far as it went this division was fairly satisfactory : it left, 

 however, a certain group of tumours in the debatable ground. 

 I refer more particularly to that group which has been studied 

 so ably by Wilms, the group to which he has given the name of 

 " Mischgeschwiilste," or mixed tumours, and to that section 

 of the Mischgeschwiilste to which the name embryoma has been 

 applied. The type example of this growth is to be found in 

 connexion with the kidneys of children and young individuals. 

 Here there develops a cell-mass formed of a mixture of several 

 distinct elements. There may be striated and plain muscle, 

 gland tubules of renal type, cells of connective tissue type, of a 

 sarcomatous type, and, very rarely, bone cells or cartilage cells 

 have been encountered. Wilms has pointed out very clearly 

 the mode of origin of these tumours. The Anlage of the glandular 

 cortical portion of the permanent kidney is of mesoblastic origin, 

 and at a very early stage in the embryo this " nephrotome " 

 is cut off or differentiated from the myotomes, or cell-masses 

 lying on either side of the median line which will eventually 

 give origin to the main musculature of the trunk axis and to the 

 bone and cartilage of the vertebral column. Now, there have 

 been cells at a yet earlier stage which have been the ancestors 

 both of the future muscle cells and of the glandular portion of 

 the kidney cells, and these ancestral cells have, by progressive 

 multiplication, given origin to both. We can best comprehend 

 the tumours in question by supposing that in the course of 

 development one or more of these ancestral cells has become 

 snared off, or has come to occupy an unusual position with regard 

 to its fellows, so that its development cannot follow the normal 

 line. We may suppose that such a cell becomes carried along 

 into the developing future kidney and that in time that cell 

 begins to grow, and in growing retains the properties and the 

 potentialities given to it at its origin. Such a " cell-rest," to 

 apply Cohnheim's term, in its proliferation will tend, therefore, 

 to produce both muscle cells and renal epithelium, and the tumour 

 derived from it will of necessity be of a mixed type. 



We encounter mixed tumours of a similar nature in several 

 parts of the body — in the parotid, in connexion with the genital 

 tract, and so on — and it is along these lines that they gain their 



