SECT. 3] AND EIGHTEENTH CENTURIES 165 



common to the viviparous, then, what is pecuHar to severall of them, 

 as, a sow, mare, cow, ewe, she-goat, doe, rabbet, bitch, and a woman, 

 lastly, what is observable in an Egg, skate, salmon, frog, etc. All is 

 illustrated with divers accurate schemes." 



The subsequent course of chemical embryology in the seventeenth 

 century may be put in a very few words. Marguerite du Tertre 

 incorporated in her obstetrical text-book of 1677 the results of some 

 similar experiments to those of Needham. "If you heat the (amniotic) 

 liquor", she says, "it does not coagulate, and if you boil it it flies 

 away leaving a crass salt like urine, but if you heat the serosity of 

 blood, it solidifies as if it were glue." The same observation was re- 

 corded by Mauriceau in 1687, who concluded, with some common 

 sense, that, as there was so little solid matter present, the liquid could 

 not be very nutritive; and by Case in 1696, who said, "In this juice 

 the plastic and vivifying force resides, for although to our eyes it looks 

 in colour and consistency like the serum of the blood, yet it is abso- 

 lutely \toto coelo] different; for if a little of the former is slowly evaporated 

 \si in cochleari super ignem defines] no coagulation will ever appear." 

 Lister said this once more in 171 1, but with Boerhaave's work of 1732 

 the subject entered a new phase. 



In 1670 Theodore Kerckring published an adequate work on foetal 

 osteology, and, two years later, de Graaf and Swammerdam, 

 making full use of the opportunities afforded them by the invention 

 of the microscope, described in detail the ova of mammalia, thus 

 demonstrating the truth of Stensen's suggestion of some years before. 

 It is important to note that these workers mistook the "Graafian 

 follicles" for the eggs — a mistake which was not rectified till the time 

 of von Baer. Stensen himself published not long after an account 

 of these eggs also, but he was by then too late to gain the priority 

 of demonstration. Portal's claim that Ferrari da Grado, who lived 

 in the fifteenth century, was the true discoverer of mammalian ova 

 has been disproved by Ferrari; and, although it is true that Volcher 

 Goiter described what we now call the Graafian follicles, he did not 

 recognise in any way their true nature. 



De Graaf 's discovery was confirmed in 1678 by Caspar Bartholinus, 

 and, in 1674, by Langly, whose original observations had been made, 

 so it was said, in 1657, the year of Harvey's death. If this is true, 

 Langly has the priority of observation, Stensen of theory and de 

 Graaf of demonstration. 



