MISCELLANEOUS: STIMULI UNDERLYING TUMOR-FORMATION 549 



seems as if they must be cross-sections of the worm rather than 

 of the host-plant. They have, however, been studied critically 

 by Nemec and I have been able to confirm many of his findings. 

 What the worms excrete into the tissues we do not know, but 

 undoubtedly, judging from the excretions of higher animals, 

 their waste products must include both acids and alkalies. Pos- 

 sibly the giant-cells are due solely to acid mouth secretions. 

 There is no reason why the different parts of the tumor might 

 not be due to different secretions, e.g., the general hyperplasia 

 to the anal excretions and the very peculiar giant-cells to the 

 mouth excretions. We shall come again to this subject of acids 

 and alkalies in connection with overgrowths, when we discuss 

 ammonia tumors, acetic acid tumors, crown galls, etc. 



If my hypothesis is correct, farther away from the feeding 

 eel-worm larvae the excreted poisons should be more dilute and 

 less active, and as the karyokinetic mechanism of the nucleus 

 appears to be more resistant to paralysis than the protoplasmic 

 membrane of the cell, since in many tumors of plants and animals 

 it is not at all interfered with, and by this I mean that in many 

 tumors there are no giant-cells, we should expect to find hyper- 

 plasia also in remoter parts of the nematode gall and also in its 

 earliest stages, and this is just what we do find (Fig. 414). Also 

 in club-root, due to Plasmodiophora brassicae, as may be seen 

 from Kunkel's photomicrographs, we find similar phenomena. 

 Moreover, in a variety of other galls, such as those due to 

 various gall flies (Figs. 415 to 424) there is a curious likeness 

 to what occurs in the nematode galls, that is, close to the 

 feeding organism where the excreted poisons are most concen- 

 trated, there is a stretching of the cells to form the so-called 

 " nutritive layer," which layer is rich in sugar, starch, oil and 

 albumen, while farther away from the larval chamber, where 

 the diffusing excretions would be weaker, there is always a 

 fine-celled overgrowth, also stuffed with foods starch, sugar, 

 etc., arranged in such a manner as to be clearly related to the 

 stationary larval cavity or cavities, a hyperplasia not developing 

 irregularly, as in tumors due to eel-worms, fungi or bacteria, 

 organisms able to move about and thus to change the direction 

 and movement of the stimulus, but always quite regular in its 



