Physical Properties of Protoplasm 163 



with considerable difficulty. The protoplasm of plant cells is much 

 more dilute or less rigid than that of animal cells. 



RESTING AND DIVIDING MALE GERM CELLS OF THE SQUASH 

 BUG (ANASA). GRASSHOPPERS AND CRICKETS 



A brief note has been published on this subject. 21 



The whole cell substance of resting and dividing spermatogonia 

 and spermatocytes is a moderately viscous gel. Cutting away pieces 

 of the cytoplasm and nucleus in Ringer's fluid shows that these struc- 

 tures are far too rigid to flow or change shape under such experi- 

 mental treatment. The appearance of a network is due to denser 

 masses of nuclear gel that grade into the diluter surrounding substance. 

 No definite threads or fibrils could be dissected out of resting nuclei. 

 Some of the optical principles involved in a study of the living nuclei 

 of spermatogonia and spermatocytes were discussed in connection 

 with the nucleus of proteus. 



Very definite statements can be made about the physical proper- 

 ties of chromosomes and spindle fibres. The chromosome has been 

 found to be the most highly concentrated and rigid part of the nuclear 

 gel. Such a mass of gel is less translucent and has a higher refractive 

 index and absorptive power than the diluter homogeneous gel in which 

 it is imbedded. A chromosome when dissected out shows no affinity 

 for water and does not disintegrate readily. tPieces of it stick to the 

 glass dissecting needle but when drawn out show no marked elas- 

 ticity. The spindle fibre is an elastic concentrated thread of nuclear 

 gel and its absorptive power and refractive index are also different 

 from those of the diluter gel in which the spindle fibre is imbedded 

 and from which it cannot be entirely freed. Metaphase spindle fibres 

 that were dissected out with great care seemed continuous with the 

 ends of the chromosomes. The homogeneous gel in which a telophase 

 spindle is imbedded is so rigid, that all the surrounding cytoplasm 

 can be cut away and the spindle and chromosomes show no appreciable 

 change; metaphase, anaphase and telophase spindles can be cut to 

 pieces in Ringer's fluid and the pieces are so rigid that they undergo 

 no change in shape. 



21 KITE and CHAMBERS: 1912, Science, N. S., xxxvi, p. 639. 



