SECONDARY TUMORS AND METASTASIS. 73 
internally developed secondary tumors contain the parasitic bacterium the same as the 
primary tumors, but it is not abundant in any of the tissues. The bacterium causing the 
disease has been found also sparingly in the strand connecting primary and !secondary 
tumors. 
Much difficulty has been experienced in stain- 
ing Bact. tumefaciens in the tissues of the daisy, and 
ideal preparations are yet to be obtained. It would 
seem from an examination of numerous slides, and - 
also from the results of many poured plates, that 
the organism occurs in the tissues of the tumor in 
rather small numbers, especially as compared with 
the organism causing the olive-tubercle. From what 
I have seen I believe it occurs only inside the paren- 
chyma cells, stimulating them to divide and passing 
on from mother cells todaughter cellsin this manner. 
The development of these tumors depends 
on a very delicate series of adjustments between 
the attacking organism and the host cells. My 
present hypothesis as to the mechanism of the 
tumor development in crown-gall is as follows: 
Through wounds which have not injured the cells 
beyond the power of recovery (needle-pricks in case 
of my experiments) the bacterium gains an entrance 
into the cell; here it multiplies rapidly for a short 
time; its further growth is checked by the appear- 
ance of acid to which it is very sensitive—this acid 
being developed in the cell as a by-product of the 
bacterial action on sugar; the first effect of the 
acid is to inhibit the further growth of the bacteria 
and consequently there never can be very many 
bacteria in any individual cell; the continued 
action of this acid on the bacteria leads to the pro- 
duction of involution forms (clubs and Y’s) and 
finally a portion of these bacteria are killed out- 
right, but the concentration of the acid is not suffi- 
cient to destroy the host cell; the nucleus of the 
latter now divides, either under the direct stimulus 
of the acid, or under the influence of bacterial 
endotoxins which now for the first time have been 
liberated, 7. ¢., have come into contact with the Fig. 24.* 
nucleus by diffusion through the permeable mem- 
branes of the dead bacteria; during the cell-division the bacteria are carried over into the 
daughter cells, where under the new conditions those not destroyed by the acid multiply 
rapidly for a short time; then in turn their growth is checked by more acid, whereupon 
ensue the other changes ending in another cell division. In this way is developed first the 
primary tumor, then the strands penetrating the sound tissues in various directions, and 
finally the secondary tumors, which I have elsewhere called metastatic tumors, but which 
are probably not so in the sense that loose tumor cells migrate from the primary tumor to 
*Fic. 24.—Leaf of Paris daisy (Chrysanthemum frutescens) developing internal tumors at points marked by letter 
x and beyond. The lower one has split open surface of rib, others are still sub-epidermal. Source of infection was 
the stem-tumor here shown, which was induced by needle-punctures introducing Bacterium tumefaciens. Photo- 
graphed Feb. 12, 1908. : 
