382 SUMMAEY OF CUKRENT EESEAECHES RELATING TO 



markings and other structural features. The inequahty increases rapidly 

 1 the end of the first year, when it reaches its maximum. Thereafter it 

 diminishes, but never disappears. 



b. Histologry. 



Visible Structure of Cell Protoplasm and its Death Changes.* — 

 Robert Chambers, jun., has studied in particular the ova of Asterias, 

 Arbacia, EchinacJinms, Gerahratulus, and Fucus. His methods are those 

 of " microdissection." " It is remarkable how much tearing and pulling 

 with a needle living protoplasm will undergo without showing injury. 

 One may puncture a cell with a needle, and drag the needle through the 

 cytoplasm back and forth, cutting through the sides of the cell, and if 

 the procedure be slow and gradual the tear closes up behind as the 

 needle proceeds, and the process may be continued almost ad libitum 

 without producing an ill effect. If, on the other hand, the needle be 

 carried rapidly through the cytoplasm, a few thrusts only are necessary 

 to induce rapid disorganization. The effects of injury are probably 

 cumulative. If injurious effects be made to follow one another without 

 giving the cell time for recovery, the additive effects of the injury soon 

 manifest themselves in disorganization of the protoplasm, resulting in 

 the death of the cell." 



The following conclusions have been arrived at in regard to the fine 

 stru(?ture of the protoplasm. Protoplasm is a hydrophilic colloid which, 

 in early germ-cells, egg-cells, and Protozoa, usually exists in the sol 

 state, with a surface layer in the gel state. Adult somatic cells generally 

 are gels in which one cannot demonstrate a cell membrane possessing a 

 consistency different from that of the cytoplasm within. 



The microscopically-visible granules in the cytoplasm of the egg of 

 Arbacia may be classified in two groups : (a) the microsomes, which are 

 considerably less than one micron in diameter, and constitute the most 

 resistant parts of the cell, maintaining themselves after its complete 

 disorganization ; and {b) the macrosomes, which range from 2-4 micra 

 in diameter, and are very sensitive to injury. 



The external surface of the egg-cell is a gel which passes gradually 

 into the sol in the interior. The surface gel is very extensile and con- 

 tractile and is readily regenerated on injury. Tearing of this surface, 

 if unrepaired, results in an outpouring of the internal cytoplasm and in 

 dissolution. 



A remarkable property of protoplasm is its ability to form a protec- 

 tive gel film not only on its external surface, but also around an injured 

 area which is in process of disorganization. The disorganized mass thus 

 insulated is eventually expelled. 



Disorganization of the cytoplasm of the egg-cells studied takes place 

 in the following way : — (1) the macrosomes swell and go into solution ; 

 (2) the liquid hyaline cytoplasm may flow out into the water or form a 

 rigid coagulated mass. The coagulation structure gradually coarsens 



* Amer. Journ. Physiol., xliii. (1917) pp. 1-12 (2 figs.). 



