218 FERTILIZATION 



This experiment by Mead was one of a number of pioneering studies made 

 during this period in an endeavor to activate artificially the egg. Another such 

 experiment was reported by R. Hertwig (1896), using eggs of the sea urchin. 

 In a strychnine solution the nucleus underwent changes preparatory to the 

 first division. Also, Morgan (1896) found it possible to produce cleavage, 

 normal and abnormal, if unfertilized eggs of the sea urchin, Arbacia, were 

 placed in sea water to which certain amounts of sodium chloride had been 

 added and then were returned to normal sea water. Morgan ('00) later 

 found that magnesium chloride added to sea water induced cleavage in eggs 

 treated for various intervals. Loeb, in 1899 (see Loeb, '06), initiated a 

 series of experiments on activation of the sea-urchin egg. As a result of many 

 similar experiments, Loeb reached the conclusion that membrane formation 

 was the essential part of the activation process in that it stimulates the forma- 

 tion of the membrane by initiating cytolysis of the egg (see Loeb's theory at 

 end of chapter). Consequently, he sought substances which would elicit 

 membrane formation and found that monobasic fatty acids, such as butyric, 

 acetic, formic, or valerianic, would produce membrane formation, and, also, 

 that ether, bile salts, saponin, etc., would do the same. However, although 

 these substances aroused certain initial activities of the egg, Loeb found it 

 necessary to apply a so-called corrective treatment of hypertonic sea water 

 to arrest the cytolytic effect of the first treatment, which, according to his 

 belief, restored respiration to its normal level. As a result, Loeb perfected a 

 treatment as follows which produced development in a considerable number 

 of sea-urchin eggs so exposed (Loeb, '06): 



(1 ) Unfertilized eggs were placed for Vz to 1 Vi min. in 50 cc. of sea water 

 to which 3 cc. of N/10 solution of butyric or other monobasic fatty 

 acid had been added. This treatment effected membrane formation 

 when the eggs were returned to normal sea water, provided the eggs 

 had been exposed long enough to the acid. 



(2) The eggs were allowed to remain in normal sea water for 5 to 10 

 min. and then were subjected to the corrective treatment in hypertonic 

 sea water, made by adding 15 cc. of IVi N. NaCl solution to 100 cc. 

 normal sea water, and allowed to remain for 20 to 50 min. Lesser 

 times of exposures also were used successfully. 



(3) Following this treatment, the eggs were returned to normal sea water. 



An example of an entirely different method from the solution technics 

 employed above on the sea-urchin egg is that of Guyer ('07) and especially 

 Bataillon ('10, 'II, '13) on the egg of the frog. The method employed by 

 the latter with success was as follows: Eggs were punctured with a fine glass 

 or platinum needle and then covered for a time with frog blood. Puncturing 

 alone is not sufficient; a second factor present in the blood is necessary for 

 successful parthenogenetic development. The number of actual developments 



