308 ON GROWTH AND OVERGROWTH 



earlier conclusions need correction. Nay, more, we already 

 possess exhaustive studies upon the various forms of tumours 

 affecting one or other organ, the mammary gland, uterus, kidney, 

 skin, etc. Taking everything into consideration, the time ought 

 to be ripe for attempting more than this individualizing method. 

 So, to repeat, I believe that we have by us embryological and 

 anatomical observations which permit us to proceed further. 

 What is more, I believe that, for a sound classification, we must 

 inevitably pass backwards to the developmental relationship 

 of the different tissues, that we must accept an embryogenetic 

 basis, but one more in consonance with our present knowledge. 



It is not necessary here to dwell upon the relationship of 

 morbid to normal processes, and to show that the former in each 

 case are but exaggerations in one or other direction of the latter ; 

 nor need I point out the importance of a knowledge of the develop- 

 ment of each tissue in arriving at a determination of the modi- 

 fications which may be undergone by that tissue. In his Middle- 

 ton-Goldsmith lecture in New York, Minot * has, during the last 

 year, treated this latter subject in so masterly a manner that 

 anything I could say would be but a feeble reflection of his 

 admirable presentation of the bearing of embryology upon 

 pathology. What I wish now to point out more especially is 

 that we pathologists — and we are not by any means the only 

 ones to blame — have during these years continued to hold fixed 

 and stereotyped views with regard to the exact nature and 

 development of the different germinal layers, and it has been this 

 misconception of these layers and the changes undergone by 

 them, and of the mode in which the various tissues have been 

 derived from them, that has brought us to this stage of discarding 

 classifications constructed along embryological lines. 



We have, that is, held as a body, that from a given layer, 

 as, for example, the epiblast, only tissues and tumours of one 

 general type are developed, and in practice we have found that 

 this is not wholly the case. We have concluded that embryo- 

 genesis is a broken reed, and this despite our willingness to dis- 

 cover in it the basis for sound classification. 



In order to indicate how a classification which is primarily 

 embryological can be developed, it will be necessary for me to 



1 " On the Embryological Basis of Pathology," Science, U.S., xiii., 1901, 

 481. 



