Physical Aspects of Protoplasynic Streaming 201 



strand are placed in separate air-tight compartments, thus permitting 

 the protoplasm to flow freely from one compartment to the other, 

 and if the air-pressure in one of the compartments is modified, then 

 the protoplasmic streaming in the connecting strand will be modified 

 accordingly. The tendency to flow from one compartment to the 

 other is thus opposed by a counter-pressure. 



In order to realize such an experiment in practice, the following 

 technique has been arrived at after repeated modifications and 

 improvements. 



II. METHOD 



(a) Preparation of the Material. The stock culture of Physarum 

 polycephalum is grown on moist filter paper and fed powdered oats 

 (Camp, 1936). Then a tiny bit, say 1/20 gram, of protoplasm is 

 removed from the stock culture and placed on the surface of nutri- 

 tion-free (tap water) 2 per cent agar in a Petri-dish. After an hour 

 or two the protoplasmic mass spreads out into a thin round sheet, 

 and later into a network or branched system of vigorous strands 

 with a wavy advancing margin or several peninsula-like expanses. 

 When a comparatively straight part is found among these vigorous 

 strands, a small rectangular sheet of agar (ca. 15 X 25 mm., 1 mm. 

 in thickness) , including the selected protoplasmic strand, is cut out. 

 This rectangular sheet of agar, containing a strand of protoplasm 

 lying parallel to its longer sides, is placed on a glass slide of 24 X 60 

 mm. (Fig. lA) . 



The next step in the preparation is to put new blobs of protoplasm 

 from the stock culture on to both terminals of the strand. The 

 strand and the two blobs of homospecific protoplasm soon fuse, and 

 the three separate parts now unite to make one dumbbell-shaped 

 Plasmodium (Fig. IB) . 



Further procedure involves inverting this glass slide with the 

 agar sheet and the dumbbell-shaped plasmodium on to a specially con- 

 structed double chamber, shown in Figure 2. The glass slide covers 

 the top of this chamber. As shown in Figure 2, two glass partitions 

 (p) 1 mm. thickness, are fastened vertically across the chamber 6 

 mm. apart from each other. As the height of these partitions is about 

 1.5 mm. less than that of the side wall of the chamber, there remains 

 just this much distance between the upper edge of the glass partitions 

 and the under surface of the slide after the latter is inverted on the 

 top of the chamber. This space will partly be occupied by the con- 

 necting strand of the protoplasm and by the thin sheet of agar that 



