ii 4 SCIENCE PROGRESS 



in the general conclusions drawn from the experiments. Some 

 of the tumours and even small outgrowths from tumours 

 represented in great detail in these drawings are less in diameter 

 than the thickness of the mouse's skin. When it is realised that 

 even a stocking will alter the relative proportions of a foot, 

 ankle and leg and that the drawings referred to were made from 

 measurements taken through the mouse's skin, the value of the 

 details becomes more than questionable. When also the impos- 

 sibility of discriminating between minute collections of tumour 

 cells and the inflammatory tissue which is constantly present is 

 taken into consideration, it becomes obvious that the estimation 

 of size and of shape must always include elements of error which 

 vary inversely with the size of the tumour. 



In primary cancer in man, a very marked feature is the in- 

 vasion of the surrounding tissues and the effect upon the general 

 health as the invasion interferes with the functions of the 

 body. This is particularly marked when ulceration and sepsis 

 occur. In the case of grafted mouse tumours the growth does 

 not invade the surrounding tissues, being cut off by the capsule. 

 Even if the surface of the tumour ulcerate and become septic, 

 the mouse does not generally seem to suffer in general health. 

 The septic products, cut off by the capsule, do not seem to be 

 absorbed to the same extent as they are in the case of cancer in 

 the human subject. Even when the tumour grows to a size 

 approaching that of the whole body of the mouse, general health 

 of the mouse frequently does not seem to be affected. 



It has been suggested in previous passages that the cells 

 forming a malignant growth, having passed out of somatic 

 co-ordination and living upon the parent organism as parasites, 

 might in a sense be regarded as separate individuals. The 

 occurrence of meiotic phenomena and other considerations were 

 cited in support of this view ; most of the experiments just 

 enumerated upon transmissible mouse tumours may be inter- 

 preted in a way that emphasises it still further. 



Variation, in so far as our knowledge goes, is an intrinsic 

 property of all living matter. Even two cells of the same organ 

 in the same individual are never the same morphologically. But 

 the differences extend beyond morphological features and include 

 potentialities of growth, resistance or susceptibility to stimuli 

 and other non-morphological characters. Moreover as existing 



