1917] CURRENT LITERATURE 339 
JENSEN thought. On the contrary, the behavior of the cell is due to an invading 
specific microorganism. These facts, together with the observation that in 
one case at least (Rous’ sarcoma of fowls) the abnormal growth can be produced 
by some sort of material separable from the cells and capable of multiplying 
when injected into other tissues, are regarded by the author as greatly advan- 
cing the contention that animal cancer is due to an intracellular parasite. 
ey anterenting results® were obtained in a series of experiments 
designed to f tumor growth in crown gall. 
In this investigation the author was guided by the hypothesis that the sub- 
stances produced in the metabolism of Bacterium tumefaciens must be the 
direct cause of the cell proliferations. To the end of determining the effects 
of such substances various plants were injected first with compounds which 
chemical studies had shown to be products of the causal organism, and finally 
with a large number of other substances. 
The first experiments were conducted with ammonia, which in various 
concentrations was injected into the stem cavity of Ricinus and into the fruit 
cavities of young green tomatoes. The result of these injections was an abun- 
dant formation of cushion-like intumescences within the cavities in both cases. 
Later, proliferations of the same type were obtained by the injection of a large 
number of other substances, including ammonium salts of organic and of 
inorganic acids, dilute solutions of the acids themselves, salts, glucose, and 
Saccharose, and in some instances to a slight extent with distilled water. In 
many cases when the tissues of the pith cavities of Ricinus were exposed to 
weak ammonia vapors from dilute solutions of ammonium phosphate or 
ammonium carbonate in tubes sealed into the hollow stems, proliferations were 
produced not only in the cavities the reagents but also in many inter- 
nodes above and below the opened one. The action in these cases, therefore, 
took place at a distance through thick partitions. The most striking result 
was obtained from the injection of a 5 per cent solution of ammonium dihy- 
drogen phosphate into a very young internode of Ricinus. In this instance the 
pith cavity became completely filled by the proliferating pith, and from this 
tissue a complete vascular cylinder was differentiated. The orientation of 
the new inner cylinder was the inverse of that of the normal cylinder, the 
phloem being at the center and the xylem occupying the outer region. Such 
a complete cylinder was observed only once, but in many instances isolated 
of the tumor strand through the tissues is not yet clear. Whether this structure 
pushes its way through the pith or cortex by apical growth after the manner of the 
internal roots of lycopods, or whether progress through the tissues is accomplished 
by successive cell-invasion by the bacteria and subsequent differentiation of the in- 
vaded cells into the characteristic tumor strand, has not yet been determined. From 
eek of his stained sections Samir thinks that both types of invasion occur. 
Erwin F., Mechanism of tumor growth in crown gall. Jour. Agric. 
mis 8:165-186. pls. 4-65. 1917. 
