Chapter III 



— 11 — 



Physical Properties 



lf.^/ 



plasm. HOFMEISTER and Berthold showed for the first time that 

 if a section is cut out of a filament of Vaucheria, a part of the cyto- 

 plasm comes out, taking a spherical form by virtue of the law of 

 surface tension which characterizes liquids (Fig. 7). Since that 

 time, many similar experiments have been performed, notably by 

 Strugger on Chara cells. And finally, an experiment by KUHNE on 

 the cytoplasm of the Myxomycetes, can be explained only by a 

 liquid state of the cytoplasm. This worker succeeded in obtaining 

 an artificial muscle by enclosing in elastic tubes, fragments of the 

 Plasmodium (intestines of Hydrophilus piceus). 



All these facts, added to those obtained by microdissection, 

 which will be spoken of further on, permit us to 

 conclude that the cytoplasm possesses, in general, 

 the properties fundamental to liquids: it flows 

 and has a surface tension which tends to make it 

 take the form of minimum surface, i.e., spherical 

 form. 



Research carried out in these later years with 

 the aid of the microdissector, put into practice by 

 Chambers, has made great progress in the knowl- 

 edge of the viscosity of the cytoplasm. This 

 method consists in the use of a special instrument, 

 the micromanipulator, or microdissector, provided 

 with glass needles which can be moved mechan- 

 ically with great precision. This permits the 

 dissection of cells under high magnifications. 



The work of Seifriz with the micromanipu- 

 lator on various plants (Mucoraceae, Fucus, pol- 

 len tubes, Plasmodia of Myxomycetes) also dem- 

 onstrates that the cytoplasm presents a consist- 

 ency which is very variable: now very fluid and 

 almost like water, now almost solid, even to the 

 state of a gel with a consistency of bread dough 

 or vaseline, in which the passage of the needle 

 leaves a gaping hole. 



The cytoplasm is very fluid in the Plasmodium 

 of the Myxomycetes as long as the latter is in an 

 active state. If the point of a needle of the micro- 

 manipulator is broken off in the Plasmodium, the cytoplasm is 

 rapidly aspirated (c/. p. 37). Its fluidity is, however, always 

 greater than that of water, intermediate between that of water and 

 that of oil of paraffin, but from the moment that the Plasmodium 

 ceases growth, i.e., in the stages which precede sporulation, the 

 consistency of the cytoplasm increases: it equals that of oil of 

 paraffin, then that of glycerin and, finally, that of bread dough. In 

 Rhizopus nigricans, the cytoplasm is also liquid in the young por- 

 tions of the hypha. It is, nevertheless, less fluid than that of the 

 Myxomycetes and presents approximately the consistency of oil of 

 vaseline. On the contrary, in the older portions of the hypha of 

 Rhizopus, the cytoplasm grows thick. Its viscosity becomes that 



// 



in 



Fig. 6. — Cyclosis 

 a staminate hair 

 of Chelidonium. The 

 arrows indicate the 

 direction of the cur- 

 rents in the various 

 cytoplasmic meshes. 

 n, nucleus. (After 

 VAN TiEGHEM and 



COSTANTIN). 



