SECT. 3] AND EIGHTEENTH CENTURIES 197 



case because Wolff was not a theorist, but rather an experimentalist; 

 his writings are marked by their abstention from the discussion of 

 speculative points. The above passage is very interesting. It reminds 

 us of the great difficulties with which the embryologists of this epoch 

 had to contend. Serial section cutting was unknown, the staining 

 of thin layers and reconstruction were unheard of; even the hardening 

 of the soft embryonic tissues was only just discovered, as is indicated 

 by Haller above. Hertwig has excellently discussed the advances in 

 embryological technique which took place during this and the fol- 

 lowing century. It is true that dyes were beginning to be used, as 

 some instances already given demonstrate, and as is seen from the use 

 of madder in the staining of bones, which began about this time, and 

 was later much used by the Hunters. Heertodt's Crocologia is im- 

 portant in this connection. Heertodt, by injecting saffron into the 

 maternal circulation, found it afterwards in the amniotic fluid, and 

 his experiment was cited by Haller in support of that theory of the 

 origin of the liquid. But the most important advance in technique 

 was the progress in artificial incubation. The art, though lost through- 

 out the Middle Ages and the seventeenth century, was now to be 

 revived. 



During this period much work was done on it. As far back as 

 1 600, de Serres had mentioned some experiments of this nature, but 

 they were not successful. "The chicks", he said, "were usually born 

 deformed, defective or having too many legs, wings, or heads, nature 

 being inimitable by art." Birch, in his History of the Royal Society, also 

 refers to it. "Sir Christopher Heydon [a relative of Digby's Sir 

 John?] together with Drebell, long since in the Minories hatched 

 several hundred eggs but it had this effect, that most of the chickens 

 produced that way were lame and defective in some part or other." 

 Antonelli states that similar trials were made at the court of the 

 Grand-duke Ferdinand II at Florence about 1644, Thomas Bartho- 

 linus gives a like account with reference to the contemporary court 

 of King Christian IV of Denmark, and Poggendorff and Antinori 

 relate that the Accademia d. Cimento, inspired by Paolo del Buono, 

 made trial of artificial incubation between 1651 and 1667. 



But the most famous of all the attempts to make artificial as suc- 

 cessful as natural incubation, were those of Reaumur, whose book 

 De I' art defaire eclore les poulets of 1749 achieved a wide renown. He 

 devotes many chapters to a detailed description of incubators of very 



