ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 657 



no more than accelerate the movements, even when they are very 

 great and rapid. 



The direction of the movements of progression changes in propor- 

 tion with the intensity and colour of the light. In general, the hacteria 

 move from less illuminated points to those which are more so, or from 

 less active rays to those of greater activity. The converse only takes 

 place when the luminous action is very intense. This results as much 

 from experiments with glasses and coloured liquids as from observa- 

 tions in the objective niicrospectruni.* In this spectrum, the bacteria 

 accumulate chiefly in the ultra red and in the orange-yellow. A third 

 maximum (much weaker) is found in the green. 



In the spectrum of gas-light, the accumulation in the ultra-red is 

 much stronger than that in the yellow ; in the spectrum of solar light, 

 the ultra-red only possesses a slight advantage in this respect. The 

 crystalline lens and the aqueous and vitreous humours of four bullocks' 

 eyes in a fresh state, having been placed in a series between the 

 gas-flame and the microspectral apparatus, this intercalation had no 

 perceptible influence on the accumulation in the ultra-red ; it was the 

 same on interposing a solution of alum in thick layers. 



The direction of the incident light appears to have little or no direct 

 influence on the direction of the movements. 



Engelmann at first supposed that B. photometricum disengaged 

 oxygen under the influence of light, and that the phenomena described 

 might be essentially referred to modifications in this production of 

 oxygen ; but this presumption has not been verified. It has been im- 

 possible to prove a disengagement of oxygen. The bacteria are also, 

 relatively, but little sensitive to differences in the tension of the 

 oxygen ; nevertheless, the increase of this tension acts, in almost all 

 respects, in the same way as the increase of the light, and vice veisd. 

 The addition of a little C0 2 acts in the same manner as a sudden 

 darkening. 



What seems most probable is that light excites in bacteria a 

 specific chemical process of a reducing character, a process com- 

 parable consequently to assimilation. Special experiments have 

 shown that the action of the light cannot be attributed to changes of 

 temperature. 



Connection of the Bacilli of Hay and of Distemper, f — In 

 pursuance of his experiments on the mutual conversion into one 

 another of the bacilli of distemper and of infusion of hay, H. Buchner 

 reports the following results of experiments. 



The original form from which the distemper-bacilli were obtained, 

 the bacterium generated in infusion of hay, and distinguished by the 

 name Bacterium subtile, is marked by an extraordinary power of re- 

 sistance to high temperature, and by having no power of causing 

 fermentation ; requiring, therefore, for its nourishment free oxygen. 

 The distemper-bacteria retain their infectious properties as long as 

 desired at a temperature of 25° C. in solution of extract of meat, 



* See this Journal, post, p. 6(J1. 



t SB. Akad. Wiss. Miinchen, 1SS2, p. 147. See Natorforscher, xv. (1SS2) 

 p. 251. Cf. tins Journal, ante, p. 89. 



