6i4 LECTURE XXXV. 



The movements of Plasmodia are directly connected with these amoeboid 

 movements'. Plasmodia arise by the fusion of numerous myxamcebse, whereby 

 a large, and sometimes even immense protoplasmic mass is formed, as to the nature 

 and movements of which I have already stated what is necessary (p. 83, Fig. 80). 

 The creeping amoeboid movement is altered in the case of plasmodia, according to 

 their size, into a more flowing one, looking in the main very like the flowing of 

 a thick tenacious slime. Of course this is only an external appearance, since, while 

 in the case last mentioned the slimy mass passively obeys external forces, particularly 

 gravitation, we are in the case of plasmodia concerned with vital movements, and 

 the mutual displacements of their smallest particles which are effected by internal 

 forces. Inside a coherent matrix, sharply defined externally, but with its outlines 

 continually changing, there are formed more fluid portions containing numerous 

 granules, which are in active streaming movements, the direction and intensity 

 of which vary (see Fig. 80 A, p. 83), though no external stimuli produce these 

 changes in any way, I demonstrated the irritability of the plasmodia to the in- 

 fluence of light fifteen years ago. If large heaps of tan, in which numerous small 

 yellow Plasmodia of the so-called 'flowers of tan' iyMthalinum septicum) are 

 contained, are placed on a plate and kept in the dark, all the plasmodia creep 

 forth in a few hours on to the surface of the tan, and there fuse into large yellow 

 masses. If the preparation is placed at the right time in a light chamber, the 



powerful attraction for water, and hence surround themselves with relatively thick watery envelopes, 

 so that the mutual attraction of neighbouring molecules, which diminishes with the distance 

 more slowly than their attraction for water, can effect only a feeble holding together of them (a slight 

 cohesion). Under the influence of these two forces an lanstable equilibrium of all the molecules of a 

 mass of protoplasm will be set up, and these will at the same time be displaceable by slight external 

 shocks, and the whole exhibit many of the properties of a fluid ; it is also to be seen why different and 

 feeble influences so easily deprive the protoplasm of a part of its water and strengthen its cohe- 

 sion. It may then be further supposed that the molecules, in virtue of their mutual attraction, 

 strive to lay themselves next one another in such a way that they turn their smallest diameters 

 towards one another, because this position ensures the closest approximation of their centres of 

 gravity. In this attempt, however, they will be in part prevented by the aqueous envelopes, and, on 

 the other hand, it may be assumed that the molecules are endowed with directive forces, so that, for 

 example, they seek in virtue of these latter to turn their longest diameters towards one another. 

 One may here indeed suppose an electric polarity to exist in the molecules. Evidently, through the 

 play of three attractions which are independent of one another in value, it would be possible for a 

 position of equilibrium to be set up in which relatively considerable quantities of energy are present 

 In the form of tension ; the most insignificant shock might here disturb the equilibrium, and a dis- 

 turbance occurring at one point must at once be propagated to the neighbouring molecules, and 

 the movement must gradually affect places further and further distant from the starting-point. If 

 the question is now raised as to the shocks which are able to set free the forces in tension in 

 this molecular system (when it is itself left in equilibrium) very different ones may be supposed. 

 Within the living protoplasm chemical processes are continually going on : these may at individual 

 places alter the molecules chemically, or increase or diminish their attraction for water, their mass, 

 or their polarity. Independently of the chemistry, moreover, small thermal, electric variations, 

 imperceptible vibrations, &c., will affect sometimes one, sometimes another part of the protoplasm 

 and disturb its unstable equilibrium.' 



' The path to our knowledge of plasmodia, so exceedingly important for the theory of proto- 

 plasm, was first opened by De Bary, in his celebrated treatise, 'Vber die Mycetozoen,' in the 

 'Zeitschr. f. wissench. Zoologie' (1857, B. 10), and a second edition, reprinted separately (1864). 

 Cf. further, Cienkowski in 'Jahrb. f. wiss. Bot.' B. III. pp. 525 and 500. Also Strasburger, 

 'Studien iiber Protoplasma; Jena (1876) ; Sachs, 'Lehrbnch; IV Aufl., p. 265. 



