ORGANIZATION OF THE BACTERIA. 37 



Cohn has first pointed out the movements of the 

 protoplasm, in which currents occur, above all in 

 the central portion, the peripheral portion remain- 

 ing homogeneous and motionless. The vacuoles 

 are also found in the central portion ; Warming, 

 however, who has observed them in Monas Okenii, 

 Vibrio rugula, V. serpens and Spirillum undula 

 var. littoreum, has sometimes seen them in the mid- 

 dle of the plasma, at another near the exterior wall. 



The granules which are seen in the protoplasm 

 were considered by Ehrenberg as stomachal vesi- 

 cles or ovules. They are of two sorts ; the one, 

 highly refractive and not bordered by a dark circle, 

 are considered by Warming as nothing more than 

 mere compact- masses of protoplasm; the second, 

 also highly refractive, but surrounded by a dark 

 circle, resemble drops of oil, and have been taken 

 for fat granules ; but the recent researches of 

 Cramer, Cohn, and Warming have proved that 

 some of them, at least, are formed of crystalline 

 sulphur. They are not soluble either in hydro- 

 chloric acid or in water, but they are dissolved in 

 absolute alcohol, in hot caustic potash and sulphite 

 of soda, in nitric acid and chlorate of potash at 

 ordinary temperatures, and in bisulphide of carbon, 

 when the membrane, which is permeable with dif- 

 ficulty, has been previously destroyed by sulphuric 

 acid. Although their small dimensions and great 

 refractive power prevent them from being dis- 

 tinguished with certainty as crystals of sulphur, as 

 they are doubly refractive to polarized light their 

 crystalline nature cannot be doubted. 



