SECT. 3] AND EIGHTEENTH CENTURIES 149 



chemistry of the appearance of haemoglobin is one of the most obscure 

 corners of chemical embryology. The older observers explained it by 

 considering the yolk to be akin to blood and ready to turn into it 

 at the slightest inducement. 



Another problem which neither Fabricius nor Harvey did any- 

 thing to solve was the nature of the air-space at the blunt end of 

 the egg. "Fabricius recounts several conveniences arising from it, 

 according to its several magnitudes, which I shall declare in short, 

 saying, It contains aire in it, and is therefore commodious to the 

 Ventilation of the egge, to the Respiration, Transpiration, and Re- 

 frigeration, and, lastly, to the Vociferation of the Chicken. Where- 

 upon, that cavity is at the first very little, afterwards greater, and 

 at last greatest of all, according as the several recited uses do require." 



As regards the placenta, Harvey took the side of Arantius and 

 denied any connection between the maternal and foetal circulations. 

 "The extremities of the umbilicall vessels", he said, "are no way 

 conjoined to the extremities of the Uterine vessels by an Anastomosis, 

 nor do extract blood from them, but are terminated in that white 

 mucilaginous matter, and are quite obliterated in it, attracting 

 nourishment from it." "Wherefore these caruncles may be justly 

 stiled the Uterine Cakes or Dugs, that is to say, convenient and 

 proportionate organs or instruments designed for the concocting of 

 that Albuginous Aliment and for preparing it for the attraction of 

 the veins." From this it would appear that Harvey regarded the 

 uterine milk as the special secretion of the placenta, conveyed to the 

 foetus through the umbilical cord. The nature of the uterine milk 

 is still very imperfectly understood (see Section 21). Its discovery is 

 usually attributed to Walter Needham, but various remarks in this 

 chapter (Ex. lxx) seem to show that Harvey was well acquainted 

 with it. In later times, it was regarded by some (Bohnius and 

 Charleton in 1686, Zacchias in 1688 and Franc in 1722) as the sole 

 source of foetal nourishment. Mercklin spoke of it in 1679 as ''materia 

 albuginea, ovique albo non absimili". Harvey often calls the placenta 

 the uterine liver, no doubt only for this reason, but the remarkable 

 appropriateness of the term was to become apparent in Claude 

 Bernard's day. As regards the matter of the continuity of the maternal 

 and foetal circulations, he criticises van Spieghel. "There came forth 

 a book of late", he says, "wrote by one Adrianus Spigelius, wherein 

 he treateth concerning the use of the umbilicall arteries and doth 



