ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 963 



collecting in enormous quantities, and moving about with great 

 rapidity wherever they come into contact with the air, and losing 

 their motility the moment this is removed. Exposed to a stream of 

 pure hydrogen they soon subside completely to rest ; pure oxygen 

 acts with greater energy than the atmospheric air. 



If a drop of defibrinated blood, which has been oxygenated by 

 shaking in the air, is run into a drop of water between two glasses 

 in which all bacteria have come to rest, they begin at once again 

 to move about actively at the point of contact of the two fluids. This 

 does not take place (or at least only at a very few points, and for 

 a very short time), if, instead of arterial blood, that is taken thi-ough 

 which a stream of carbonic oxide has been passed immediately before. 

 If, instead of the drop of oxygenated blood, green cells, such as 

 Euglena, a piece of a filamentous alga, or a brown diatom like 

 Navicula, are brought into contact with the drop containing motion- 

 less bacteria, and observed under a cover-glass with a magnifying 

 power of 200-300, the bacteria are seen immediately to begin to 

 swarm in gi'cat quantities about these cells, while in all other parts 

 of the drop they are completely at rest. If the field of view is now 

 suddenly darkened, but not so much as to prevent the bacteria from 

 being still distinctly visible, the swarming bacteria at once come to 

 rest, either remaining stationary at the same spot, or dispersing 

 themselves through the fluid by molecular motion. When the light 

 is again let in, the motion recommences. 



The only satisfactory explanation of these phenomena is that the 

 chlorophyllaceous cells give out oxygen under the influence of light, 

 and that this is the cause of the movements of the bacteria, and of their 

 collecting round the spot where it is given ofi". 



The following are some of the results of the application of this 

 test obtained by Engelmann. 



All chlorophyllaceous cells of both lower and higher plants give 

 off oxygen in the light, even when the ordinary green colour is 

 replaced by brown, as in diatoms, or by olive-green or light green, 

 as in many Flagellatfe and Oscillatorieae. The same is the case with 

 chlorophyllaceous animals, as Paramecium hursaria, Hydra viridis, and 

 Spongilla, sometimes very energetically. 



The parenchymatous cells of the leaf of seedlings of Nasturtium 

 grown in the dark, which contain etiolin but no chlorophyll, when 

 brought into moderately strong light, momentarily exhale oxygen. 

 But after exposure to the light for an hour at a uniform temperature 

 of 21"^ C, the yellow colour- of the cells was not sensibly altered. 



The energy of the evolution of oxygen in diflerent kinds of cells 

 is greater the larger the amount of chlorophyll, or of other colouring 

 matter with the same physiological properties. It is, for example, 

 very great ru Euglena viridis, or in young cells of Zygnema ; small in 

 cells of Spirogyra where the chlorophyll-bands are narrow and some 

 distance apart, and in the guard-cells of the stomata of the leaf of 

 Tradescantia. No evolution of oxygen takes place from cells with 

 colourless protoplasm, as monads, amoebfe, the mycelial filaments of 

 moulds, the root-hairs of Hydrocharis, the colouidess cells of the 



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