284 GENERAL PHYSIOLOGY 



effective constituent, at least for animal-cells, can be very easily 

 removed and replaced by hydrogen, it is only necessary to prepare 

 chemically pure hydrogen by means of Kipp's apparatus and con- 

 duct it through a closed gas-chamber. The most convenient gas- 

 chamber for microscopical investigations is that devised by 

 Engelmann (Fig. 129, /). The cells to be investigated are placed 

 in such a chamber and observed in a hanging drop of the liquid 

 in which they live. By a series of experiments Kiihne ('64) has 

 shown that after replacing the air by hydrogen Amoeba gradually 

 suspends its movements after about 24 minutes. From this 

 condition it can be brought back to life by a renewal of atmo- 

 spheric air. But, if it remains for some time longer in the 

 absence of oxygen, it dies. The movements of large plasmodia of 

 Myxomycetes in a medium free from oxygen often cease only after 

 three hours, and later the plasmodia die. 



For the study of the question how the two phases of contraction- 

 movements, namely, expansion and contraction, are influenced by 

 the withdrawal of oxygen, the most favourable objects are marine 

 Rhizopoda, possessing long pseudopodia, over which the movement 

 of each particle of protoplasm is extended for a very considerable 

 distance. Such a one is Ehizoplasma Kaiseri, a naked rhizopod 

 possessing a nuninucleated, orange-red cell-body , from which radiate 

 out in all directions fine, anastomosing pseudopodia, in which the 

 protoplasmic streaming is uncommonly active (Fig. 130, /). If a 

 Rhizoplasma l be placed in the Engelmann gas-chamber and a 

 current of oxygen be passed through, after one and a half to three 

 hours the effects of the withdrawal of oxygen become noticeable. 

 The centrifugal current in the protoplasm, which before was very 

 active, so that the pseudopodia were extended, becomes feebler 

 and feebler and finally ceases. But the centripetal current con- 

 tinues for a while longer, so that the pseudopodia slowly shorten : 

 gradually, however, the centripetal current also diminishes and 

 soon is scarcely noticeable. The protoplasm has accumulated, at 

 the places where the pseudopodia branch, into tiny masses, which 

 are not spherical and spindle-shaped, as when contracted because 

 of strong stimulation, but are more pointed, angular and toothed. 

 In this form the Rhizoplasma is finally completely motionless (Fig. 

 130, 77). Specimens possessing shorter pseudopodia finally draw 

 them completely in. Hence, by the withdrawal of oxygen, the 

 phase of expansion (the centrifugal protoplasmic streaming) first 

 comes to a standstill, and then gradually the phase of contraction 

 (the centripetal protoplasmic streaming). If now atmospheric air 

 be introduced, after about five minutes tips of new pseudopodia 

 begin to project from the central cell-body. After about 

 ten minutes, active streaming is again apparent upon the old 

 pseudopodia. A new current from the centre appears upon them, 

 1 Cf. Verworn ('96, 3). 



