230 



In the broad lueaning which we have given to the con- 

 ception of stimulation ve will have to include also as s 

 airimulus effects those processes of growth, which, accord- 

 ing to Weigert-^ tn^d numerous other pathologists, can not 

 he traced hack to the action of a formative stimulus, hut 

 which are caused hy the removal of an;r kind of hinderanoes 

 to growth . According tov'/eigert we are concerned In all 

 laWorraal tissue proliferation with phenomena of gror^th etc. 

 made impossible under normal oonditiona of life end a normal 

 cause of development by all kinds of impedimenta. The re- 

 moval of any opposition is evidently equivalent to the 

 change in the effective fnotops, (external end. internal). 

 According to our definition of the preoessea 'of stimulation 

 (ai^oy and its causes, no reason exists fop explaining the effedts 

 of groT/th which ape ©atised by the removal of impediments, 

 as other than the stimulus effects. 



Be will soon return to the question as to whether there 

 are norcEil plant tls'sues of whioh the formation mr.y be ex- 

 plained by the removal of any opposition to growth. 



We have termed stimulus the change in any active factor, 

 but not every change Of external conditions causes reaction on 

 the part of the cells,- many a chanfee, which acts as a cause of 

 stimulation in definite kinds of cells, does not come into ques- 

 tion at all as such in cells of a different nature. In short,- 

 ©ach reaction presupposes a definite qualification of the cells, - 

 without a capacity for reaction there is no reaction . 



The spores of the fern usually germinate very quickly when 

 strevm on a nutrient solution,- provided they are exposed to 

 the light. The spores react by growth to the stimulus brought 

 about by the absorption of food stuffs, after the light has 

 made the cells capable of reaction. As has been shown, in tnis 

 case the capacity of the cells for reaction may oe ^^^^^S"* „^„ 

 about also by increases of tempera ture^. The spores of mosses 

 feel this same necessity fa>r light,- in them, this capacity for 

 reaction can also be produced^ by a supplying ^'i*J- f ^f ^^ : _ f^ 

 most cases we find that the reaction capacity of the cells is 

 dependent tn definite conditions. The supplying of energy iS 

 supposedly the chief cause in its production, and :f^en ^^^l-*-??^ 

 the consumption of energy in the reaction *», ^^f ^i^^^^^ihout 

 should be observed here th?.t the energy supplied ^^<'JJ^^5°JL. 

 is not convertible in every form for the cells, nor transverti- 

 ble into potential energy. 



Distinction must be made between an ^^^^f ^^^i^J^S^SerL 

 for reaction, explained by a temporary lack of potential energy. 



and a specific incapacity remaining P«c^'-^j;^^nfl«?inite changes 

 which are provided with potential energy. ^^^J^.J^fj^^Jlnds of 

 in the factors cause stimulation reactions in definite^Kinab^u* ^ 



I'ueue Fragesteilungen in'der pathologischen Anatomie. 

 OeB. d«»u.tfloher Naturf. u, Aerzte, " Verhandl. 1896. 



2 Forest Heald, Gametophytio Eegeneration, Leipzig, 189V. 



3 Further examples on "the ^Preparatory" influence of light 

 and other factors in Klebs, Beding. d. Fortpfl. bei eintgen 

 Algen u< J?ilzen, 1896. 



