miscellaneous: stimuli underlying tumor-formation 567 



There must be also defective respiration and loss of water 

 leading to concentration of cell-sap and increased acidity in 

 Wolf's wounded cabbages and my wounded cauliflowers already 

 referred to as developing intumescences. 



It is possible also that the tumor-producing action of ammo- 

 nia is not very unlike that of the acids I have mentioned. It is 

 likely that it w^ould combine at once on entering the living cell 

 with some one of the acids always present and act as an acid 

 salt. The organic acids most likely to be present in plants 

 attacked by crown gall are malic acid and citric acid, and the 

 ammonia salts of these acids act in the cell, I believe, like acids. 

 It is true they both give an alkaline reaction with Congo red or 

 methyl orange but these are indicators which, so to speak, ig- 

 nore the acid part, being interested only in the ammonia of the 

 salt. If we use phenolphthalein as indicator they both give a 

 strongly acid reaction, but here, again, the indicator may be said 

 to ignore the other partner in the combination, being interested 

 only in the organic acid. None of these indicators can, I think, 

 be depended upon for the purpose required. Litmus is a much 

 better indicator for this purpose because it is a plant product 

 and both ammonium malate and ammonium citrate, so far as 

 tested, react acid to neutral litmus paper. What is still more to 

 the point, they both react acid to the hot w^ater extract of the 

 anthocyan from red cabbage, which is the same species of plant 

 as the cauliflower on which I have produced the ammonia tumors. 

 Up to this time I have not been able to find out what organic 

 acids occur in cabbages and cauliflowers, but malic acid is of 

 almost universal distribution in plants and citric acid is common, 

 so that it is probably one of these two. But even if the ammonia 

 acts on the cell directly as an alkah there will be afterward, ac- 

 cording to my ideas, an increase in acidity due to loss of water 

 through the disturbed hyaloplasm, and in any event there will 

 be disturbed respiration. 



In the production then of these weak acids and alkalies 

 out of place or in excess in certain tissues we have, it would seem, 

 the key to the whole tumor situation. Given a multiplying and 

 feeble parasite, that is, one able to produce these substances in 

 stimulating (membrane paralyzing) amounts and at the same 



