676 SCIENCE PROGRESS 



The idea that the cells of malignant growths have escaped 

 from control and live in a parasitic manner upon the parent 

 organism forms the essential basis of most of those theories as 

 to the nature and origin of cancer that have met with any very 

 general acceptance. Therefore, though the hypothesis that the 

 cells of cancer have passed out of somatic co-ordination was, I 

 believe, first formulated by me in the particular sense suggested 

 here, 1 I can claim but little originality with regard to the idea. 

 Many explanations both before and since have been based upon 

 ideas fundamentally similar in meaning, though they vary more 

 or less in mode of expression and are influenced by the special 

 points of view and the particular facts emphasised by the person 

 who enunciates them, the latest of this group of hypotheses 

 being that of the late Sir Henry Butlin 2 , who developed the 

 idea to the further stage of describing the cancer cell as a para- 

 sitic protozoon (unicellular animal) derived from the tissue cells 

 of the host and even went so far as to give the various forms it 

 adopts generic and specific names. 



James Ewing 3 gives a very excellent account of the develop- 

 ment of this class of hypothesis from Cohnheim's theory of 

 embryonic inclusions. He shows how the theory of " Cell 

 Autonomy " has grown gradually and regularly from this origin. 

 By " Cell Autonomy " he implies something very similar to what 

 I had already called " Somatic Co-ordination." 



It is necessary here to consider the capacity to undergo 

 differentiation which exists in the cells of the fully formed 

 multicellular organism. 



We have already seen that the bodies of multicellular animals 

 are built up from the cells derived from a single cell, the fertilised 

 ovum. The earlier generations of cells are all very much alike ; 

 it is only when the development of the embryo has advanced to 

 a considerable extent that the different groups of cells destined 

 to form the various tissues of the body begin to differ in shape, 

 size and other characters. When the body is completely formed, 

 it contains within it cells which differ from each other to an 

 extraordinary degree, bearing but little resemblance either to 

 each other or to the ovum from which they were derived. Now, 



1 Essentials of Cytology (1907) and elsewhere. 



2 "Two Lectures on Unicellula Cancri,'' Brit. Med. Journ. Nov. 25, Dec. 2, 



1911. 



3 " Cancer Problems," Arch. Internal Medicine, vol. i. 1908. 



