LIMITING FACTORS IN THE HISTORY OF SCIENCE " 



his secretary Eckermann on October i8, 1827.1 He said little while 

 Eckermann told him about the habits of the cuckoo and other birds, 

 but when Eckermann related how he had liberated a young wren 

 near a robin's nest and how he had found it subsequently being fed 

 by the robins, Goethe exclaimed: "That is one of the best ornitho- 

 logical stories I have ever heard. I drink success to you and your 

 investigations. Whoever hears that, and does not believe in God, 

 will not be aided by Moses and the prophets. That is what I call the 

 omnipresence of the Deity, who has everywhere spread and implanted 

 a portion of His endless love." And so it always was with the theo- 

 logical naturalists; they hailed with enthusiasm the discovery of 

 monogamy in tortoises, or mother-love in goats, but they had nothing 

 to say concerning the habits of the hookworm parasite or the appear- 

 ance of embryonic monsters in man. Not until the beginning of the 

 nineteenth century did it become clear that nature cannot be divided 

 into the Edifying, which may with pleasure be published, and the 

 Unedifying, which must be kept in obscurity. 



The Balance of Thought and Observation. 



In the end we may say that the progress of a branch of natural 

 science such as embryology depends on a delicate balance of three 

 things; speculative thought, accurate observation, and controlled 

 experiment. Any modification of the optimum balance will act as a 

 powerful limiting factor on progress. Speculative thought, in par- 

 ticular, has shown a tendency to crystallise too readily into doctrines 

 which, by way of attachment to some philosophical or theological 

 issue, live a longer life than they deserve. Thus the Aristotelian theory 

 of the formation of the embryo by the coagulation of the menstrual 

 blood, built in the first instance upon a faulty deduction, became 

 incorporated in the Aristotelian tradition oi forma and materia^ and 

 although quite repugnant to observation, remained the official theory 

 throughout the European middle ages, and apparently in perpetuity 

 in India. So powerful was the rationalism of a medical education at 

 about 1630 that the physicians to whom Harvey demonstrated the 

 empty uteri of the King's does preferred to believe their books rather 

 than the evidence of their senses. 



The account given by Harvey himself (1653, p. 416) cannot be 

 omitted ; 



^ Conversations with Goethe, Everyman edition, p. 243. 



