Manchester Memoirs, Vol. Ixii. (191 7), No. 2 29 



Theory of Loeb. 



Loeb's, early experiments were undertaken to discover the 

 action of various acids on the unfertilised eggs of sea urchins. 

 He found that cell cleavage could be) induced by the action 

 of HC1, HNO3, H 2 Si0 4 , etc., but after a few cleavages had 

 occurred disintegration followed. Further development up' to 

 the plutei stage was effected in the original method by the use 

 of a hypertonic solution of sea-water. The concentration of 

 normal sea- water was raised 50 per cent, by the addition of 

 sodium chloride. Unfertilised eggs were placed in this solution 

 for two hours and then removed to normal sea-water. By further 

 experiment it was found that practically any salt, so long as not 

 actually poisonous, would effect the same result provided that 

 the concentration of the water was raised 50 per cent. Thus it 

 seemed that the stimulus for development was not due to any 

 specific action of certain salts but to a change in the osmotic 

 pressure. 



When eggs are fertilised by a sperm there is produced 

 round the egg a membrane, known as the fertilisation 

 membrane, also the eggs rise to the surface of the liquid. These 

 two results of fertilisation were not produced by the artificial 

 method described above. This led Loeb to devise a fresh series 

 of experiments. Eggs of Strongylocentrotus purpuratus were 

 placed for one minute in a solution Of 500 cc. of sea-water to 

 which 3 cc. of a decinormal fatty acidi had been added. The 

 fertilisation membrane was produced, but segmentation did not 

 occur. If, however, after being thus treated they were placed in 

 a hypertonic solution of sea-water the eggs developed. This 

 result was obtained with many of the monobasic fatty acids, such 

 as formic, acetic, propionic, butyric. Summarising the results 

 of many observations, we may say that substances causing 

 haemolysis also cause membrane formation, for instance, saponin, 

 bile salts, hydrocarbons, ether, etc. 



The theories that Loeb has formulated are many, but they 

 are all purely chemical. The membrane formation was first 

 supposed to be produced by the liquidation of fatty substances 

 which are resident on the egg surface. As a corollary of its 

 formation oxidations are set up in the' eggs, which' if allowed 

 to continue cause disintegration, and finally the death, of the 

 eggs so treated. These oxidations are caused because the fatty 

 substances round the egg prevent the diffusion of OH ions, but 

 acids and the substances favouring membrane formation dissolve 

 the surface fats and render the .egg permeable to the action of 

 ions. The action is further supposed to consist in their com- 

 bination with the albuminoid substances in the' e.gg to< form new 



