256 LEIGH HOADLEY. 



of the fertilization reaction. As soon as the initial part of the 

 reaction is completed, i.e., as soon as the membrane has raised, 

 the metallic concentration which has formerly been inhibitory in 

 its action ceases to be wholly effective and some of the eggs may 

 develop as far as the motile free-swimming forms in the solution. 

 In the following pages, such a concentration, which inhibits the 

 elevation of membranes, when eggs are inseminated in it, will be 

 termed "membrane-inhibitory." Such inhibition of membrane 

 elevation is complete. If, however, the concentration of the. 

 salt is greatly increased, a concentration may be reached at 

 which cleavage in turn is completely inhibited, but here again, 

 the time factor is important. For example, if a given concen- 

 tration is toxic to cleavage for a set of eggs transferred to it five 

 minutes after insemination in normal sea water, it is said to be 

 "cleavage-toxic." It may allow 40 per cent, to 50 per cent, 

 cleavage if eggs are transferred to it 20 minutes after such an 

 insemination, or even 95 per cent, if they are transferred after a 

 30-minute interval. In such a case, second cleavage will be 

 completely inhibited. When cleavage is used as a criterion of 

 toxicity, the period of exposure to the solution will vary ac- 

 cording to the length of time elapsing between insemination 

 and transfer. If, when eggs are transferred to the solution 

 five minutes after insemination, first cleavage is inhibited, then 

 it follows that eggs transferred at a later time will not perform 

 second cleavage, though they may cleave once. 



McGuigan ('04), v. Euler and Swanberg ('21), Olsson ('21), 

 and others have investigated the effects of the salts of certain of 

 the heavy metals on enzyme action. Mathews ('04), working 

 with Fundulus, compares the physiological action of the heavy 

 metals with their solution tensions. It was with the same idea 

 that McGuigan worked on the ferments. He found that, 

 generally speaking, a low solution tension was indicative of great 

 toxicity. There were, however, certain exceptions to the series. 

 v. Euler and Swanberg attribute the poisonous effect of the salts 

 to their property of binding certain groups of the enzyme mole- 

 cule and thus making it ineffective. 



In the ferment experiments just cited as well as in the experi- 

 ments made by Mathews on Fundulus, the experiments allowed 



