miscellaneous: stimuli underlying tumor-formation 563 



control. Later the tumor as a whole might show increased alka- 

 linity, since the organism causing it also produces ammonia, and 

 changes in the tumor tending toward decay are always on the in- 

 crease. Some of the steps in this process remain to be worked 

 out experimentally but we may suppose that they exist and occur 

 in about the follow^ing order: (1) increased acidity (H-ionization) 

 due to bacterial excretions; (2) paralysis of the protoplasmic 

 membrane leading to increased cell permeability; (3) loss of water 

 from the parasitized cells; (4) concentration of cell sap; (5) form- 

 ation of cell precipitates; (6) disturbance of transpiration; (7) 

 disturbance of respiration; (8) increase of peroxidases and in- 

 crease of respiration due to (9) repeated karyokinetic cell- 

 division during which food-stuffs are consumed; (10) compensa- 

 tory return flow of water and food-stuffs into the tumor favoring 

 continued rapid growth, which is also favored in later stages 

 by continued superficial loss of water. 



A number of more or less well established facts, some of 

 which I have already mentioned, point to these conclusions. 

 For instance, we know^ that in flasks of tap-water containing 

 peptone and grape sugar the crown-gall organism produces 

 ammonia, aldehyd, acetic acid, and formic acid, and there is every 

 reason to suppose that if it can produce these substances in a 

 flask it can do so in the plant, and that these are the substances 

 which cause the development of the hyperplasia, since I have 

 shown that each one of these substances is capable of producing 

 small hyperplasias when vaporized or sprayed upon susceptible 

 plants. Sugar is abundant in crown galls, often so abundant 

 that it cannot all be used in growth and consequently a portion 

 of it is re-converted into starch and deposited in the tissues, 

 much as glycogen for the same reason, is stored in animal can- 

 cers. Sugar is very abundant in acid potato shoots giving rise 

 to intumescences (p. 541). It is also abundant in the frost 

 tumors (Harvey). Peroxidases are abundant in crown galls 

 and also in the frost tumors. There is, undoubtedly, acceler- 

 ated respiration in all tumors but who can say whether it is a 

 cause or a consequence of the abnormal growth? I have indi- 

 cated how I think it occurs, namely as a response to oxygen- 



