THE CAUSATION OF DISEASE. 355 



is capable of surviving under conditions in which the epithelial 

 cannot. How well this is shown in the example already 

 quoted, of the fibrous degeneration of old age, when, owing to 

 the imperfect cell-E consequent upon failing blood-making and 

 blood-carrying organs, the fibrous tissue develops at the ex- 

 pense of the epithelial. 



The presence of the carcinoma parasite is not incompatible 

 with the growth and multiplication of epithelial cells ; on the 

 contrary, under the general disturbance of bacterial irritation, 

 their activities are actually hurried on, and a more or less 

 crude form of gland is produced, and the dissolutionary nature 

 of the process shows itself chiefly in the imperfect arrangement of 

 the cells. Whether the epitheliomata are caused by a different 

 parasite from the acinous varieties I will not venture to say, but 

 all the latter are probably produced by the same organism. 



In the sarcomata, on the other hand, the bacterial irritation 

 is so virulent that under it only the most elementary forms of 

 connective tissue can survive. Inasmuch as this latter order of 

 tissue is everywhere present, there is no very pressing reason 

 to suppose a special tissue habitat for this organism. How far 

 the varieties of sarcomata are due to differences in the organ- 

 isms causing them it would be difficult to decide, for who can 

 say how far the type of malignant tissue is determined by the 

 structural proclivities of the tissues affected, and how "far by 

 specific parasitic action ? Certain it is, however, that the structural 

 differences of the sarcomata are very largely due to corresponding 

 differences in the bacteria causing them ; thus the small, round- 

 celled variety is probably due to an excessively virulent parasite — 

 one so virulent, indeed, that it permits the survival of the most 

 rudimentary order of tissue only. That, on the other hand, the 

 nature of the tissue affected plays a part in determining the 

 type of morbid tissue, is shown by the fact that myeloid sarcoma 

 most frequently originates from the medulla of bone where 

 giant cells abound, and the melanotic variety solely from the 

 pigmented tissues. This fact is equally well shown in the case 

 of the carcinomata : the primary cylindrical-celled epitheliomata 

 originate in tissues containing cylindrical epithelial cells ar- 

 ranged in tubular glands, and the primary squamous variety 

 solely from tissues containing squamous epithelia. 



