NATURE OF AGENTS WHICH FORM MEMBRANES 451 



acids is far greater than it is in the case of the fatty acids. In fact one- 

 thousandth normal Butyric Acid is more efficient in inducing membrane- 

 formation than twelfth normal Hydrochloric Acid ; yet hydrochloric acid 

 of even this concentration does not injure the eggs in the periods of 

 exposure requisite, because normal fertilization by sperm can still 

 occur in 100 per cent, of the eggs treated in this manner, and weaker 

 concentrations of hydrochloric acid, which are usually ineffective in 

 causing membrane-formation, are, of course, even less toxic. A very 

 convincing experiment devised by Loeb to illustrate this point consists 

 in adding a little Sodium Butyrate to a solution of hydrochloric acid 

 in sea-water which is otherwise incapable of causing membrane-for- 

 mation. The mixture immediately becomes an effective membrane- 

 forming agent, although its acidity, if anything, has been reduced. The 

 introduction of the sodium butyrate leads to an interaction with the 

 hydrochloric acid, setting free a little butyric acid which accomplishes 

 the initial stage of fertilization. 



It had been observed in 1887 by O. and R. Hertwig.that if sea- 

 urchin eggs be immersed in sea-water saturated with Chloroform 

 and only a trace of this substance will dissolve in sea- water fertili- 

 zation-membranes are formed. It had also been found by Herbst 

 that Benzene, Toluene and Creosote have a similar action. In all these 

 cases, however, the membrane-formation was found to be rapidly suc- 

 ceeded by Cytolysis and the disintegration of the eggs, so that develop- 

 ment, of course, did not occur. Loeb found however, that if the eggs 

 be exposed only for very brief periods to these solutions and then 

 transferred to normal sea-water a percentage of the eggs will form 

 membranes without cytolysis and may subsequently be induced to 

 develop by treatment with hypertonic sea-water. It is a curious, and 

 as yet unexplained fact that whereas eggs immersed in butyric-acid 

 sea-water do not form fertilization-membranes until they are trans- 

 ferred to normal sea-water, eggs treated with sea-water containing 

 benzene or amylene form membranes before they are removed from 

 the mixture. 



The various reagents which were thus found effective in inducing 

 membrane-formation have this in common, that they are all fat- 

 solvents or highly soluble in fats and furthermore they are all in greater 

 or less degree Hemolytic Agents, that is, substances which are capable 

 of dissolving red blood-corpuscles. This fact drew attention to the 

 possibility that other hemolytic agents might be capable of exerting 

 a like effect upon the unfertilized egg of the sea-urchin. 



According to Koeppe, besides heat and alternating electric currents 

 there are five distinct groups of chemical agents which are distinguished 

 by their power of inducing hemolysis of red blood-corpuscles or, more 

 generally, Cytolysis of all types of living cells. These are: 1. Certain 

 specific substances, for example the series of glucosides comprising 

 the Saponins and Solanins, or the Bile-salts. 2. A series of Fat-sol- 

 vents such as benzene, ether or alcohol. 3. Distilled water, 4. Hydro- 



