Jan. 29, 1917 
Mechanism of Tumor Growth in Crowngall 
175 
tissues reacted least to the most injurious substances—that is, to ammo¬ 
nium oxalate, ammonium chlorid, and ammonium nitrate. 
I then determined on these plants the action of various dilute pure 
acids, the same being distilled water solutions of the acid component of 
the salts already tested, viz, uric acid, carbonic acid, tartaric, citric, 
acetic, butyric, lactic, oxalic, formic, succinic, salicylic, sulphuric, 
hydrochloric, and phosphoric acids. 
It would take too long to describe in detail all of the experiments with 
acids which consumed a whole summer and were also unexpectedly posi¬ 
tive—that is, showed quite clearly that galls or intumescences may be 
caused by the action of many dilute acids, including such as various 
bacteria, larvae of gall flies, and other parasites are able to produce, and 
that the previous response to the ammonia salts was not exclusively a 
response to the alkaline element in them but might be a response due 
to the combined or joint action of these substances on cells young enough 
to respond to it. 
Very fine intumescences were obtained in this way by injecting 10 per 
cent solutions of the organic acids—that is, uric acid, malic acid (PI. 10), 
citric acid, and tartaric acid. Often the whole wall of the pith cavity 
was covered with them, and there were frequently large outgrowths 
around the needle wound where it entered the pith cavity (PI. 11). But 
also I obtained intumescences with sulphuric acid and with phosphoric 
acid and sparingly even with distilled water. These results were unex¬ 
pected and at first disconcerting, it must be confessed, for I had not then 
read Toeb's latest remarkable book on parthenogenesis, wherein are 
detailed many positive and splendid results with acids on animal eggs (15), 
and which would have advanced my work by at least two years had I 
read it when it first appeared. I was looking for a specific chemical effect 
as tumor cause and I discovered instead a general physical (osmotic) 
effect as cause. I will not undertake to explain the specific action on 
the cell of all these various substances, since Toeb has speculated on this 
subject better than I can hope to, and since I have seen nothing to con¬ 
tradict his hypotheses. Much remains for the future, so far as an under¬ 
standing of the exact mechanism of cell division is concerned, but Loeb 
seems to have made out quite clearly that the stimulus which sets unfer¬ 
tilized eggs to growing is a purely physical one—that is, an increase in 
the osmotic pressure of the solutions in which they are placed causes loss 
of water from the egg surface with the formation of a membrane, which 
is the beginning of cell division. I believe increased local osmotic pres¬ 
sure also explains the results I have obtained, as well as those which 
occur naturally in tumors. It is*the beginning, I think, of all tumor 
growth. 
If these things are so, why, then, does not the injection of any organ¬ 
ism produce a tumor? This is a proper question and may be answered 
tentatively as follows: (1) In many cases the injected bacteria do not 
