192 THE SCIENCE OF BIOLOGY 



of normal processes. The experimental initiation of develop- 

 ment supports the hypothesis that spermatozoon brings to 

 ovum a minute quantity of an unknown, but no doubt dis- 

 coverable, substance which furnishes a necessary link in 

 the chain of causation that initiates development. If a sub- 

 stance, isolated from the spermatozoa, could be brought in 

 contact with eggs and thus cause them to develop, 6 the 

 stimulus to development would be recognized as a specific 

 substance. Fertilization would then lose that intangible 

 quality which in the past has cast a spell of mystery over so 

 many biological phenomena. Research of this nature is now 

 being carried forward by so many investigators that we may 

 hope for a comprehensive understanding of this first step 

 in development, although the facts now established have 

 already raised unsuspected problems. 7 



The work upon artificial parthenogenesis has illuminated, 

 but not explained, the process of normal fertilization. What 

 is called the fertilization reaction between egg and sperm 

 must be attacked by experimental work upon the normal 

 activation of the ovum by the spermatozoon. The story 

 of the work now in progress is too extensive to be related. As 

 one investigator puts it, "the main physiological problems 

 of fertilization are still before us; all the work has merely 

 prepared the way for their solution. Fertilization is the 

 knot in the webs of successive generations which must be 

 untied before we can trace the strands from generation to 

 generation." For the purposes of our present discussion, 

 the history of the fertilization problem shows the biological 



6 Cf. the work of O. C. Glaser, " Fertilization and Egg-secretions," Biol. 

 Bull., Aug. 1921. 



7 Considerable notoriety attached to the work upon artificial parthenogenesis 

 when the results of the first successful experiments by J. Loeb became 

 known. Newspaper feature stories hailed the accomplishment both as an ex- 

 planation of the immaculate conception and as a creation of living protoplasm. 

 The latter interpretation was manifestly ridiculous, since what had been done 

 was to artificially stimulate an already living egg to develop as it would have 

 done under normal stimulation by the spermatozoon. 



