miscellaneous: tumors in absence of parasites 483 



in the pith (Fig. 363) but no islands of wood in the bark. The 

 experiment, however, should be repeated especially on plants 

 with a thicker and firmer bark. In most if not all of my at- 

 tempted bark inoculations the fluid ruptured to the surface and 

 escaped. 



As in tyloses, so in crown gall we are forced to conclude that 

 it is not the mere presence of the bacteria in the tissues that 

 leads to the overgrowth, but rather the stimulus of certain prod- 

 ucts of their metabolism. Theoretical considerations led me 

 to ask the chemists of the Department of Agriculture to make 

 analyses of flask cultures of Bad. tumefaciens and on the basis 

 of their findings I experimented with various plants subject 

 to crown gall, using dilutions (fluids, vapors) of irritating sub- 

 stances said to be present in the cultures. With these I ob- 

 tained many striking small overgrowths (hyperplasias) and little 

 or no evidence of wounding. Such responses were obtained 

 with ammonia (Figs. 364, 365), acetic acid (Figs. 366 to 372), 

 aldehyd (Fig. 373), and formic acid (Figs. 374 to 377)— all said 

 to be crown-gall products. All these tumors are chlorophyll 

 free, even when arising in tissues full of leaf-green. 



Many years ago Hermann von Schrenk showed that in- 

 tumescences could be obtained on cauliflower by the use of 

 copper salts, and I have seen them on amaryllis sprayed with 

 Bordeaux mixture, but, of course, our interest in artificial hyper- 

 trophies and hyperplasias centers chiefly around the question 

 of their production with substances which are the by-products 

 of parasites. In my first cases, as already stated, I did not detect 

 any killing when vapors or large fluid dilutions were used, but 

 with MacCarty's findings in mind (Mayo Laboratories 0, that 

 in very early stages of breast cancers he was able always to 

 detect a trace of cell-injury preceding the development of the 

 malignant cells, I repeated some of my experiments, studying 



1 For list of Dr. MacCarty's suggestive papers on cancer see references at 

 end of the second one I have cited under "Literature." 



carbonate by Carohne Rumbold. (See her paper in Jour. Am. Phil. Soc.) The 

 wood occupies the upper one-half of the field and is bedded against the outer face 

 of a row of hard bast fibers, the original location of the cambium from which it 

 developed. Photographed by the writer from one of Dr. Rumbold's sections. 



