190 



THE CELL AND PROTOPLASM 



the first to show a negative charge of chro- 

 matin in animal cells. This is ]iot qnite 

 true. Not long ago, I was showing the 

 lantern slide of Chnrney and Klein's ex- 

 periment at Princeton University when Dr. 

 Dahlgren called my attention to an observa- 

 tion he had made in 1915 on the nerve cells 

 of the electric ray. Although Dahlgren 

 was not interested in the question of elec- 

 tric charges, his observation clearly agrees 

 with the later work of Churnev and Klein 

 (Fig. 1). 



linizing the protoplasm (Fig. 2). Thus, 

 in sea-urchin eggs or in amebae the en- 

 trance of alkali into the cell causes a re- 

 markable increase in the free fat. In 

 ameba, at least, alkalinization is not the 

 only means of causing fat release. Irradia- 

 tion with ultraviolet is also effective (Heil- 

 brunn and Daugherty 1938), as well as 

 certain other factors now being studied. 



In summary, it may be stated that the 

 protoplasmic colloid is essentially lipopro- 

 tein ratlier than protein; that its micellae 



Fig. 1. The results of the passage of an electric current through two nerve cells of Toi-prdo ocrllaia. 

 The nuclei have migrated to the cathode, and the chromatin to ihe anode (after Dahlgren). 



As noted previously, the protojilasmic 

 colloid is not just protein, but contMins fat 

 or li])id as well. Much of the fat appears 

 to be bound chemically in some sort of 

 protein-lipid combination. Tlie amount of 

 free fat within a cell varies markedly. In 

 cells undergoing fatty degeneration, the 

 increase in visible fat is due pi-imarily 1o 

 a release of f;it from protein-lipid combi- 

 nation. Such a release can be accomplished 

 (Heilbruiin 193()) ex])erimentally by alka- 



are probably charged positively (except 

 when carbon dioxide is absent) ; and that 

 the interioi- of cells is often fluid, within 

 a cortex whose rigidity depends on the 

 presence of calcium. 



In studying an inanimate colloid it is a 

 simple matter to test the effect of various 

 i-eagents. Living cells ai'e nnicli moi-e dirti- 

 (Milt to study. For ir the ]>rotoplasin, or 

 a pari of llie |)roto|)lasiii. is changed from 

 fluid sol 1o i-iiiid uei, this mav not involve 



