562 SCIENCE PROGRESS 



that grow from the mammary gland as one organ is from the 

 other. And tumours that grow from such organs as the 

 thyroid or prostrate are so different that they can scarcely 

 be brought into the ordinary system of classification. Every 

 organ and every tissue has its own kind of tumour which is 

 peculiar to it. 



The structure of tumour buds depends upon that of the 

 parent stem. It is never so perfect or well formed, but there 

 is always a general resemblance. The clinical character of 

 the tumour, however, whether it is malignant or not, depends 

 upon the degree of maturity that had been reached by the 

 parent cells when the bud began to grow. Tumours may 

 assume many different forms — a form that grows fast or a 

 form that grows slowly ; a form that remains circumscribed 

 and limited or a form that retains its embryonic characteristics, 

 spreads in all directions and invades other organs. If the 

 parent cells are still in the actively growing embryonic stage 

 when the tumour bud is formed, the tumour bud will be 

 embryonic too. If they have already reached adult age, the 

 bud will increase in size with proportionate slowness, and 

 push surrounding structures to one side. Every organ and 

 every tissue developed from the somatic cells has its own 

 kind of tumour bud, which, according to the degree of maturity 

 of the parent cells at the moment of its birth, may be benign 

 or malignant, or benign first and malignant afterwards, or 

 so evenly balanced between the two that it is impossible to 

 say to which side it belongs. Malignant growths are not a 

 separate class of tumours but a phase that occurs in all classes. 



The Influence of Development over the Power of 



Direct Reproduction 



The power the tissues possess of reproducing their like 

 and that of giving birth to tumour buds rise and fall together. 

 They both vary inversely with the degree of specialisation 

 that development has reached. The higher the grade of 

 specialisation the more their capacity decreases. But there 

 is one material difference between them. In the one case the 

 newly formed cell merely replaces another from which it is 

 so slightly different that they can scarcely be distinguished 

 apart. In the other a new cell is born which from the first 



