LIFE AND EXPERIMENT 



ment. Whilst the doubt as to the identity in behavior of 

 excised and of intact tissues does not deny the value of 

 studies on the former for laboratory exercises, it should be 

 borne in mind that only rarely and with great difficulty can 

 these tissues be experimented upon in situ (in their normal 

 surroundings). There is doubt that results from experi- 

 ments made on tissues in vitro (excised) could be obtained 

 from such experiments made on tissues in situ. With the 

 egg the situation is different. We can speak with more 

 certainty concerning its normality for in many cases nature 

 gives us the opportunity easily to study it 'S'n situ^ This 

 advantage of a study in situ is also offered by many proto- 

 zoan cells. The control of normality in them is even less 

 difficult than in eggs, because they lack, even those with 

 most complex life-history, the potential diversity of the 

 egg-cell realized as development unfolds; the protozoan 

 cell reduplicates itself only. This difference, however, 

 though showing the greater difficulty in the study of eggs, 

 indicates the greater possibilities of such study. Valuable 

 as studies on Protozoa doubtless are for both biology and 

 medicine, they lack direct bearing on the grand problem 

 of biology, how out of a single egg arises the complex multi- 

 cellular organism. Only in the egg and its development 

 can we hope to trace to its source the pattern of structure, 

 and to resolve into its motif the harmonious behavior 

 which characterizes the many-celled animals. 



If the condition of the eggs is not taken into account, the 

 results obtained by the use of sub-normal eggs in experi- 

 ments may be due wholly or in part to the poor physiologi- 

 cal condition of the eggs. Thus, the failure of sea-urchin's 

 eggs that are freed of their jelly, fully to separate their 

 vitelline membrane after fertilization, as they normally do, 

 does not mean that the experimental removal of jelly 

 renders membrane-separation impossible but only that the 



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