EFFECTS ON MITOSIS, GROWTH, DIFFERENTIATION 963 



ferent mechanisms, and possibly simultaneous attacks on different metabolic 

 or functional systems would be particularly toxic. 



Jones (1946) studied the effects of several metabolic inhibitors on the 

 fresh-water stickleback Gasterosteus aculeatus. When Hg++ is present at 0.02 

 mikf, there is a temporary stimulation of respiration (+ 20-30%) at 10-20 

 min, followed by a depression that reaches 50% at 55 min, the fish surviv- 

 ing for 110 min. During the phase of respiratory increase, there is accelerat- 

 ed motility, a greater opercular activity, and a faster heart rate; it is quite 

 possible that the rise in respiration is associated with the greater functional 

 activity. If the Hg++ is removed after the respiration has been depressed 

 50%, recovery is slow and erratic, and the respiration never recovers its 

 normal level, although after 1 day the fish appear normal. The mechanism 

 by which the fish are killed is unknown but possibly it is asphyxial. 



EFFECTS ON MITOSIS, GROWTH, AND DIFFERENTIATION 



If SH groups are particularly important in cell cleavage, as many have 

 believed, the mercurials should be effective growth inhibitors and perhaps 

 useful agents to determine if these SH groups are enzymic or involved in 

 cytoplasmic structure. The rather potent inhibition of the proliferation of 

 many microorganisms by mercurials has been known for almost 100 years 

 and will be discussed in the following section, while here we shall attempt 

 to analyze the mechanisms by which mitosis of plant and animal cells is 

 disturbed by the mercurials. 



Eggs and Embryos 



Mercurials at concentrations in the range 0.001-0.01 mM usually inter- 

 fere with cleavage, even in sea water and despite the fact that much of the 

 mercurial in most work is removed from the medium because of binding. 

 Thus Mathews (1904) showed that the formation of embryos from Fundulus 

 heteroditus eggs is 50% blocked by 0.0048 mM Hg++, 90% blocked by 

 0.0095 mM, and completely blocked by 0.014 raM. The effects of mercurials 

 on eggs and embryos at different stages of development may be quite com- 

 plex. Hg++ may be parthenogenetic in that it induces membrane elevation 

 in Arbacia eggs and initiates a form of cleavage at 0.01-0.1 mM (Heilbrunn, 

 1925). The membranes begin to rise 3-5 min after addition of Hg++ and 

 after 12 min the cells may become constricted unequally or cleave, but the 

 relation of this to normal division is not clear. Hoadley (1930) studied these 

 effects more closely and observed that 0.025 mM Hg++ (a concentration 

 several times that suppressing cleavage completely) caused, after mem- 

 brane elevation, a clumping of the cortical pigment to one side of the egg, 

 followed by an unequal constriction which pinches off a small fragment 



