lyOOJ BllCROSCOPlCAL JOUENAL 277 



for some time that lower organisms that are ca[)able of 

 independeut movement, such as amceba, infusoria, bacte- 

 ria, and others, are attracted by certain chemical substan- 

 ces. For instance, if a capillary tube be filled with a weak 

 solution of potassium chlorate or peptone and put into a 

 drop of water in which bacteria are moving, after a few 

 seconds these will be seen hastening to the mouth of the 

 tube where they will assemble. The amoeba and the naked 

 little masses of jelly (plasmodia) of the myxomycetes 

 (mucus fungi) creep in a peculiar way by stretching forth 

 their arms or feelers toward the stimulant. This faculty 

 of being attracted by certain substances is called chemo- 

 taxis. Chemotoctic susceptability is evidently an advan- 

 tage for the creatures in question, as it leads them to good 

 nourishment and keeps them near it. Recently Professor 

 Julius Bernstein of Halle, made the discovery that a drop 

 of mercury can make very similar movements. The start- 

 ing point of his observations was afforded by an experi- 

 ment made by Poalzon in 1858. The latter put a drop of 

 mercury into a little fiat vessel, poured dilute sulphuric 

 acid over it and then laid small crystal of potassium 

 bichromate immediately beside the mercury. The result 

 was a periodical change in the shape of the drop of mer- 

 cury, which alternately approached the crystal, flatten- 

 ing itself in front, and receded from it. This was due to 

 the fact that, aided by the acid, the potassium bichro- 

 mate oxidized the neighbouring surface of the mercury 

 and thus diminished the surface tension of the side of the 

 drop. As soon as the peroxide of mercury, which had been 

 produced, dissolved in the sulphuric acid, the surface of 

 the mercury became metallic again and its tension in- 

 creased. In the first instance the mercury flowed toward 

 the crystal, in the second it sprang back. 



I explain this motion not by the physical theory purely 

 nor by the botanical theory, for I do not see how that can 

 explain it, nor by the physiological theory forthat neither 



