CHARACTER OP THE TUMOR. 169 



crushed tissue ample time to diffuse out into the bouiUon by letting 

 it stand for half an hour or an hour before the plates are made. This 

 is additional proof that the number of viable and stainable bacteria 

 in any given portion of the tumor tissue is rather small, so as to be hard 

 to find, unless it be that the bacteria are abundant but intracellular 

 to sucli an extent, i. e., so intimately mixed with the protoplasm, 

 that they do not readily diffuse out of the partially crushed tissues. 

 Certainly there is nothing in the crown-gall comparable to the phe- 

 nomenon seen in the nitrogen tubercles of legumes where the hyper- 

 trophied cells become gorged with bacteria, easily seen as such 

 whether stained or unstained. With good technique the right 

 organism can be obtained by means of poured plates from almost 

 any rapidly proliferating part of the crown-gall tumor, but often 

 not at all if one tries from older portions of the growth, i. e., those 

 more remote from the active centers of growth. 



The isolations are also sometimes complicated by the fact that 

 of two colonies on an agar poured plate looking just alike, one may 

 be able to cause the disease and the other destitute of pathogenic 

 properties. 



The difficulties we have encountered in determining the etiology 

 of these tumors make it only reasonable to suppose that similar diffi- 

 culties would be encountered in isolating the parasites of animal 

 tumors, admitting for the time being that they are due to organisms. 

 This is also suggested by the past difficulties encountered in deter- 

 mining the cause of tuberculosis, lepra, and syphilis. A few sugges- 

 tions may be offered for the consideration of pathologists who believe 

 malignant animal tumors to be of parasitic origin, but have not been 

 able to demonstrate the suspected parasite. 



(1) All present cellular theories of cancer origin are incompetent 

 to explain how such cells originate, i. e., become cancerous, or why 

 they multiply; and in the light of the facts here presented we would 

 suggest that renewed search be made for a parasitic organism or 

 virus either independent of specific ceils or confined to them and 

 using them as a means of dissemination. It would seem that the 

 initial cancer cell or cells in an organism most result from the action 

 of a foreign organism or virus, whatever may be thought of the 

 process of abnormal growth once established. 



(2) If we may assume the suspected parasite to be present in the 

 tissues in an active state in very small numbers only, owing to the 

 nearly balanced struggle of the host against the invading organism, 

 and the rapid destruction also of the causative organism in many 

 parts of the tumor, owing to the invasion of saprophytes, then one 

 might well have failed to produce the disease by injection of small 

 quantities of ground-up cells without this being conclusive evidence 



213 



