454 PROCESSES INFERRED FROM INDIRECT OBSERVATION 



and removal to normal sea-water is not essential, but, unlike the mem- 

 brane-formation by saponins it is not followed, in undiluted blood at 

 least, by subsequent cytolysis. As we shall see, however, dilution of 

 the blood by sea-water enables the cytolytic effect to appear, complet- 

 ing the analogy to the action of the saponins. As in all the instances 

 previously considered, membrane-formation is succeeded by one or 

 two cell-divisions and then by death and disintegration of the eggs, 

 unless they are treated with hypertonic sea-water which enables them 

 to develop and give rise to normal embryos. 



Loeb sought for the origin of the differing action of the various sera 

 by endeavoring to modify it, and he found that preliminary heating 

 of the sera greatly enhanced their ability to induce fertilization. Pre- 

 liminary treatment of the eggs, however, was found to be even more 

 effective. This treatment or "sensitization" of the eggs consists in 

 exposing them for a brief period to an isotonic solution of a chloride of 

 an Alkaline Earth, calcium, strontium or barium. Of the three, however, 

 strontium is much the most effective; the efficiency of barium might 

 possibly exceed even that of strontium if it were not for the fact that 

 barium is also exceedingly toxic for the eggs, while strontium is almost 

 harmless. After exposure to the Strontium Chloride and subsequent 

 transference to isotonic blood-serum, membranes are formed in nearly 

 every case upon 100 per cent, of the eggs. It has been shown by A. R. 

 Moore that this sensitization by strontium is due, not to any irreversible 

 change induced in the egg itself by strontium, but more probably to 

 the actual presence of the strontium within the egg, for if the eggs 

 after exposure to the strontium chloride solution be washed free of the 

 solution by two or three changes of sea-water, their sensitiveness to 

 blood-sera is lost. 



The membrane-forming substance in blood-serum was found by 

 Loeb to be remarkably resistant to heat. Exposure of ox-serum to a 

 temperature of 73 for half an hour, which leads to coagulation of the 

 serum-proteins, does not destroy its fertilizing power. Heating the 

 serum to 100 does, however, destroy the active substance. The blood 

 of Dendrostoma still retains a proportion of its membrane-forming 

 power, even after having been heated rapidly to boiling point; more 

 prolonged boiling (2 to 3 minutes), however, destroys its activity. 

 The thermostabile character of the active substance at once distin- 

 guishes it from the Alexin or bactericidal substance which is present in 

 mammalian blood-seia, for this is inactivated by heating to 56. 



The active substance in mammalian sera is not extracted by shaking 

 the serum with Ether. If several volumes of Acetone are added to 

 the serum, the precipitate which results, after drying, powdering and 

 resolution in sea-water, retains the power of inducing membrane- 

 formation. The substance is therefore precipitated by acetone. 



A very minute and intensely active fraction may be prepared from 

 mammalian blood-sera by the following procedure. One hundred c.c. 

 of ten per cent. Barium Chloride solution are added, with constant 



