Jan. 29 ,1917 
Mechanism of Tumor Growth in Crowngall 
I7r 
would depend on a variety of external conditions and of interrelations 
and interreactions between the host and the parasite, such as darkness, 
sunlight, heat, cold, presence or absence of oxygen, abundant or scanty 
food supply and water supply, inherited or acquired host resistance,, 
varying normal alkalinity or acidity of the tissues, inhibiting action on 
the bacteria of the acid by-products of bacterial growth, etc., ample to 
explain all the observed variations in the rate of growth of crowngalls 
and of all other neoplasms. If, furthermore, we take into account the 
various kinds and degrees of reaction on the part of the host, as we must, 
then this hypothesis is ample to explain also the whole tribe of benign 
tumors and all receding malignant growths. 
It seemed to me, therefore, that ammonia or some salt of ammonia 
must be the determining factor in tumor growth. If so, then by inject¬ 
ing dilute ammonia water into growing plants one ought to obtain, not 
typical tumors, of course, for that involves the idea of a weak continuing 
action, hard to bring about experimentally, but an active proliferation 
of cells for a short time, corresponding to the brief action of the injected 
substance. Some killing of tissues should be expected at the points 
injected, especially from action of the stronger solutions but at a distance 
where there would be feebler action, and generally with weak solutions 
there should be no wounding or killing effect, but only a very marked 
cell proliferation. I reached this point in my reasoning before I made 
any experiments. Some things I overlooked, as will be seen later. 
I was supported in these conclusions by the following facts out of 
literature. As a boy I read in some boys' wonder book that coffee ber¬ 
ries, said to be proverbially slow to germinate, might be germinated 
overnight by throwing them into strong ammonia water. I bought some 
ammonia with my first pocket money, tried it, and found it to be as 
stated, but I held no checks. That was 50 years ago. Recently I have 
repeated the experiment with the same results. I have extended the 
experiment also to date seeds and to some others known to be hard to 
germinate—that is, black-locust seeds, but only with doubtful results, and 
even in the case of coffee seeds some germinate promptly in distilled 
water, so that, curiously enough, the experiment which more than any 
other determined the trend of these researches would have had no influ¬ 
ence on my thinking had it been made in the first place properly—that 
is, with a sufficient number of controls in pure water. 
Furthermore, in 1903-1905 (7, 8), Dr. Hermann von Schrenk, of the 
Missouri Botanical Garden, observed numerous warty proliferations on 
the leaves of cauliflowers which were attacked by Peronospora parasitica 
and had been sprayed with the fungicide copper ammonium carbonate, 
and investigated their origin with the following results: 
In his experiments Dr. von Schrenk readily obtained numerous warty 
growths on cauliflower leaves within five days' time by spraying upon 
them copper ammonium carbonate. He also obtained warts by the 
