L. V. HEILBRUNN. 



Sensitization with Strontium Chloride. The process of sen- 

 sitization was originally used by Loeb, later by Robertson, to 

 induce the "formation" of a membrane in eggs exposed either 

 to blood sera or to various tissue extracts, all dissoved in what 

 was essentially a NaCl solution isotonic with sea-water. The 

 method employed consists either of adding 3/8 M SrCl 2 directly 

 to the serum, or of placing the eggs first into the 3/8 M SrCl 2 

 for several minutes, then into the serum. In the first paper 

 of this series I urged that SrClo caused a precipitation of sul- 

 phates and that much of the effect of sensitization was no 

 doubt due to this action. In the summer of 1913, I was able 

 to prove the truth of this statement. On July 31, 10 c.c. of 3/8 

 M SrCl 2 was added to 90 c.c. of sea-water. The voluminous 

 precipitate of SrSO 4 was allowed to settle and filtered off, but 

 the precipitate still continued to settle from the filtrate. When 

 eggs were placed into this filtrate membrane swelling occurred, 

 and this was followed by cytolysis. In another experiment, 

 the eggs were placed first into 3/8 M SrCl 2 and then into a 

 0.55 M NaCl solution. Used alone, the NaCl solution did 

 not cause membrane swelling when two drops of a thick egg 

 suspension were placed into 75 c.c. of it. But when several 

 drops of egg suspension were placed into 3/8 M SrCl 2 , and then 

 after five minutes, 2 drops of liquid containing eggs were taken 

 from the SrCl 2 solution and placed into the NaCl solution, 

 membrane swelling could be observed to take place in the eggs 

 so transferred. The vitelline membrane could be seen slowly 

 to increase in thickness, so that after about half an hour a good 

 proportion of the eggs were surrounded by a transparent outer 

 layer which bore a close resemblance to an elevated membrane, 

 except for the fact that the inner boundary of such a membrane 

 was absent. The membranes produced as a result of the "sen- 

 sitization" process did not collapse in the presence of a colloid. 

 They were also sticky, and as a result the eggs tended to aggluti- 

 nate. Such an agglutination of eggs with swollen membranes ' 

 has no doubt led Robertson ('12) to the view that "fertilization 

 and agglutination are similar phenomena." 



from Le Chatelier's theorem that whenever the pressure on a system in equilibrium 

 is diminished, a change or reaction ensues which is accompanied by increase of 

 volume. Hence the swelling. 



