DISCOVERY 



73 



maining stationary in size, they begin to grow slowly. 

 Bleeding occurs with or without injury, and the dried 

 blood forms a black, hard incrustation or scab. When 

 this is removed, a raw ulcerated surface is exposed. 

 The margins of the ulcer are thickened and hard. On 

 microscopic examination the thickening is seen to be 

 due to multiplication of the cells of the outer layer of 

 the skin. Instead of covering in the defect in the 

 surface as described for the healing of a small abrasion, 

 the cell masses are arranged irregularly, and break 

 down nearly as soon as they are formed. In this way 

 the ulcer continues to spread, always surrounded by 

 a wall of irregularly built up skin. If nothing be done 

 to arrest its course, severe blood-poisoning sets in, 

 due to the entrance of bacteria into the blood-stream, 

 or a large blood-vessel is involved by the friable 

 newly-formed epithelial cell-masses and death results 

 from hemorrhage. 



Such a progressive cellular overgrowth is described 

 as cancerous, and the description given for cancer 

 of the skin applies, with slight modification, to cancerous 

 ulceration of the lip, tongue, stomach, and intestines. 

 In parts remote from the body surfaces growth ex- 

 tends in all directions fairly equally, and the newly- 

 formed cells, even if they break down, are not removed, 

 so that the resulting mass is approximately spherical. 

 Varying resistance of the parts encountered by the 

 growth in its progress causes departure from the simple 

 geometrical form. The one constant character common 

 to all is the continuous new formation of cells going on 

 till death results. 



It will have been noted that emphasis was laid on 

 the long duration of the irritation which precedes the 

 definitely cancerous stage in the evolution of the skin 

 warts produced by paraffin. This is a very common 

 feature in the antecedent history of cancer in many 

 parts of the body. As is only natural, this is especially 

 noticeable in cancers on the surface of the body, since 

 the ease of observation permits us to recognise shght 

 degrees of damage which might not reveal their pre- 

 sence in the deeper parts. Long-continued or chronic 

 irritation, then, is a very frequent precursor of cancer, 

 and this necessity for a considerable lapse of time for 

 chronic irritation to end in cancer is probably one of the 

 main reasons for its predilection for later hfe in man and 

 animals. The kinds of irritation may be very varied, 

 provided they are not too severe and last a long time. 

 They may be chemical, as we have seen in paraffin 

 cancer and pitch warts, or soot which produces the 

 very fatal chimney-sweep's cancer. Radiant energy 

 is responsible for cancer of the shins of railway-engine 

 drivers, for cancer of the chest opposite the opening 

 of the burnous of the Soudanese, or X- rays for cancer 

 on the hands of X-ray operators. The irritation of 

 animal parasites has been followed by cancer of the 



tongue and stomacli of rats (Spiroptera cancer), and of 

 the urinary bladder in the human subject (Bilharzia 

 cancer), and so on. From this great variety it can 

 be seen that measures for the prevention of cancer 

 cannot be divorced from those needful for the 

 general improvement of the conditions of life. In 

 accordance with this. Dr. Dublin has found a greater 

 hability to cancer in American wage-earners than in 

 those in easier social circumstances, and Dr. Stevenson 

 has shown that the ma.ximum number of ('deaths 

 from cancer in public institutions in this country 

 tends to occur at ages definitely lower than in the 

 general population. 



Keeping in mind the facts that cancer begins in a 

 circumscribed area and increases in size by a con- 

 tinuous multiplication of cells, the cru.x of the problem 

 presented by it is seen to be: How are the cells in 

 the localised area concerned, started on their altered 

 tempo of growth, and why are they unaffected by the 

 restraining influence which normally holds the cells 

 of the rest of the body within their proper bounds ? 

 It would be very natural to assume that a weakening 

 of the restraint which the cells of the body exert on 

 each other is merely a part of the general weakening 

 of the natural forces accompanying old age, in which, 

 as already noted, cancer is progressively more likely 

 to develop. A special circumstance has enabled us 

 to eliminate this possibility, rendered unlikely by 

 the fact of the circumscribed origin of these growths 

 and the rarity with which they attack more than one 

 tissue in the same individual. The circumstance 

 alluded to is the occurrence in certain animals of 

 cancerous growths which can be grafted successfully 

 into normal animals of the same species. Most of this 

 work has been done with mice and rats. A careful 

 day-to-day study of the site of inoculation shows that 

 there is no question of the cells of the inoculated 

 animal's body becoming cancerous. What happens is 

 that the cells introduced continue to grow until they 

 form large masses of cells. The process can be re- 

 peated indefinitely in a succession of mice. It is not 

 even advantageous to select old animals. Grafting 

 succeeds better in young ones. Clearly, then, the 

 rapid and continuous growth of cancer cells cannot be 

 due solely to the weakening of the restraining influence 

 on growth in the body of the cancerous subject. On 

 reflection, there seems to be no escape from the conclu- 

 sion that the cancer cells behave as tliey do because they 

 are different from their neighbours. They have under- 

 gone a change in becoming cancerous, by which they 

 no longer respond to the influences wliich restrain and 

 regulate cell-division and growth in the body. Whether 

 this change is a real increase in the energy with which 

 the cells take in food and grow, so that the restraining 

 influence is powerless to hold them in check, or whether 



