138 



PHYSIOLOGY OF NUTRITION. 



arrest the growth, bat it is resumed when the seedlings are 

 subsequently placed in distilled water. 



I have also placed soaked seeds of Pisum sativum in water, in 

 flat glass dishes, near which was placed another dish containing 

 chloroform, the whole being then covered with a bell-glass. At 

 a moderate temperature (18 C.) not a single seed germinated. 2 

 We can readily demonstrate in lecture the poisonous effect of 

 chloroform 011 plant cells, by pouring some chloroform into a flat 

 dish and placing this under a bell-glass together with a leaf of 

 Begonia manicata, the leaf-stalk of which dips into water (see 

 Fig. 48). The leaf becomes discoloured, because the protoplasm 



of the chlorophyll grains is. killed, 

 and hence becomes permeable to 

 the acids of the cell-sap, which can 

 new decompose the chlorophyll. 3 



In order to ascertain whether 

 particular substances prejudice or 

 completely arrest the development 

 of Penicillium or of bacteria, we 

 conduct cultures in the manner in- 

 dicated in 35 and 38, but adding 

 to the food solutions definite quan- 

 tities of the substances (e.g. cor- 

 rosive sublimate, Salicylic acid, etc.) 

 whose effect on the fungi is to be 

 tested. Control experiments, in 

 which the poisons are not added to 

 the solutions, will, of course, be necessary. 



Thus, for example, one lot of Pasteur's food solution contain- 

 ing cane-sugar (for composition of the solution, see 18), after 

 being put aside for eight days, had become very turbid owing to 

 copious development of bacteria, while another portion of similar 

 composition, except that some 0'2 p.c. Salicylic acid had been 

 added to it, remained clear. 



To ascertain the influence of poisons on Spirogyra or other algae, 

 we place single filaments of the plants in the solutions, e.g. solu- 

 tions of Copper sulphate, Oxalic acid, etc. 4 If the solutions are 

 not too strong, so that the poisonous action proceeds slowly, the 

 first effect is generally a shrinking of the nucleus and swelling of 

 the chlorophyll bodies. 



FIG. 48. Apparatus for investigat- 

 ing the action of chloroform on plant 

 structures. 



