CONDITIONS OF CELLULAR IMMORTALITY 55 



suitable chemical treatment, such, as lack of oxygen, KCN, 

 or chloral hydrate. A typical experiment of this kind 

 made upon the sea-urchin, Strongylocentrotus purpuratus 

 may be quoted: 



were fertilized with spgrm and put eleven minutes later into 

 three flasks, each of -which contained 100 o. o. of sea-water + 16 o. c. 2-1/2 

 m CaCla. One flask was in contact with air, while the other two flasks 

 were connected with a hydrogen generator. The air was driven out from 

 these two flasks before the beginning of the experiment. The eggs were 

 transferred from one of these flasks after four hours and fourteen minutes, 

 from the second flask after five hours and twenty-nine minutes, into normal 

 (aerated) sea-water. The eggs that had been in the hypertonic sea-water 

 exposed to air were transferred simultaneously with the others into 

 separate dishes with aerated normal sea-water. The result was most 

 striking. Those eggs that had been in the hypertonic sea-water with air 

 were all completely disintegrated by "black cytolysis." Ten per cent, 

 of the eggs had been transformed into "shadows" (white cytolysis). It 

 goes without saying that all the eggs that had been in the aerated hyper- 

 tonic sea-water five and a half hours were also dead. The eggs that had 

 been in the same solution in the absence of oxygen appeared all normal 

 when they were taken out of the solution, and three hours later — ^the 

 temperature was only 15°C. — they were all, without exception in a per- 

 fectly normal two- or four-cell stage. The further development was also 

 in most cases normal. They swam as larvse at the surface of the vessel 

 and went on the third day (at the right time) into a perfectly normal 

 pluteus stage, after which their observation was discontinued. Of the 

 eggs that had been five and a half hours in the hypertonic sea-water 

 deprived of oxygen, about 90 per cent, segmented. 



Let US consider one more illustration from Loeb's 

 work in this field. Normally, in the forms with which 

 he chiefly worked, sea-urchin, starfish, and certain mol- 

 luscs, an absolutely essential condition for the continua- 

 tion of life of the germ-cells after they are discharged 

 from the body is that two cells, the ovum and the sper- 

 matozoon, shall unite in normal fertilization. Put in 

 another way, parthenogenesis does not normally occur in 

 these forms. Fertilization is an essential condition for 

 the continuation of life and development. But Loeb's 



