Protoplasmic Streaviing — Relation to Gel Structure 133 



The foregoing reaction is exhibited most strikingly in the case of 

 Ainoeha duhia. With Amoeba jjroteus the formation of the terminal 

 spheres is not so well marked and requires slightly higher pressures. 

 In this case and in the case of the amoebocytes of the body fluid 

 of Arbacia the sudden collapse of many of the pseudopodia is repre- 

 sented chiefly by an abrupt shrinkage in length. In all cases, how- 

 ever, the cells gradually become spherical if the high pressure is 

 maintained. 



A similar phenomenon has been observed by Kitching and Pease, 

 '39, who studied the behavior of the tentacles of the suctorian 

 protozoa. Ephelota coronata. In this case the disintegration, which 

 occurred mainly at pressures between 6,500 and 8,500 lbs. /in., - 

 was so complete that the suctorial processes broke up into tiny 

 isolated beads of protoplasm. This difference is probably due to the 

 greater length of the tentacular processes and to the absence of a 

 visibly differentiated surface membrane such as is present in the 

 Amoeba. 



(2) Indications of a gradient in the tensile properties of the 

 plasmogel 



It is significant to note in the Amoeba experiments that the 

 rigidity of the plasmagel varies somewhat in different parts of the 

 pseudopodium. Thus in a newly formed pseudopodium, which is 

 actively extending at the moment of compression, the terminal 

 sphere may involve all but a short remnant at the base, whereas in 

 older less active ones, only the distal tip may be involved. Assuming 

 that pressure produces the same percentage loss of rigidity in all 

 parts of the plasmagel system,^- these observations indicate that 

 normally the plasmagel is more fluid in the more recently formed 

 parts of the pseudopodium. They also support the view of Mast 

 ('26) , namely, that a gradient of rigidity exists in the plasmagel 

 tube, decreasing as one proceeds from the base to the tip of the 

 pseudopodium. 



(3) Measurement of the solating effect of the pressure 



The experimental results (Brown and Marsland, '36) , which 

 clearly describe the solation of the plasmagel as a function of 

 pressure, are given in Figure 2. The gelation percentages^^ are 

 taken to be in proportion to the time of centrifugation" required for 

 the formation of a standard hyaline zone (see Fig. 3) , measured 

 at each of the indicated levels of pressure. 



The formation of the hyaline zone (Fig. 3) requires the displace- 

 ment of all the formed bodies originally present in this region of the 



