SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 629 



toxic effects were annulled by traces of potassium cyanide, so that, 

 if the increase in respiratory rate was prevented, development would 

 go on normally after the removal of the operating substances. The 

 rise in oxidation intensity produced by ions of the heavy metals was 

 naturally very interesting, in view of the fact that, not long before, 

 traces of silver had been found by Herbst and traces of copper by 

 Delage to be parthenogenetic agents. 



Parthenogenetic agents fall into five groups : 



1 . Hypertonic solutions (Loeb) . 



2. Hydroxyl ions (Loeb). 



3. Traces of heavy metals (Herbst; Delage). 



4. Fat-soluble acids (Loeb). 



5. Fat-soluble substances such as alcohol, benzene, etc. (Hertwig; 



Herbst; Loeb). 



Of these the first three were now found by Warburg to have a strongly 

 stimulatory action on the respiratory rate of the fertilised eggs, while 

 the last two had the opposite effect. Loeb had indeed found that, 

 for the last two, the presence of oxygen was unessential, and that 

 they would produce their parthenogenetic effect anaerobically. "The 

 first group", said Warburg, "act primarily on the oxidations, from 

 which follows a change in the cell-membrane and hence a change 

 in metabolic rate. The second group act primarily on the membrane 

 and not on oxidations." These researches of Warburg led to a long 

 series of papers by various authors, arising out of the antagonism 

 between sodium chloride and cyanide in affecting the respiration 

 intensity of echinoderm eggs. Loeb & Wasteneys in 19 10 went into 

 the subject, and concluded with Warburg that the respiratory rate 

 of eggs stimulated by salt solution was depressed by the cyanide, so 

 that the toxic action of the sodium chloride was averted. But they 

 disputed many of his other statements, and a polemic followed, which 

 must be read in the original, and cannot here be discussed, as it was 

 largely concerned with matters of technique. During the course of 

 it many new facts came to light about the general effects of salt 

 action on protoplasm. Loeb found that the toxic effects of many 

 agents (neutral salts, sugars, hypertonic and hypotonic solutions, 

 chloral hydrate, phenylurethane, chloroform and alcohol) on the 

 fertilised Arbacia ^gg could be prevented by agents such as cyanide, 

 which depressed the intracellular oxidations. That this was not 



