220 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii 



hairs in the meconium of a calf embryo with a white hide. Both 

 Aides and Swammerdam had found the same thing, but Aides did 

 not think it of any significance, and Swammerdam merely remarked 

 that the calf must lick itself in utero. 



More interesting was W. Watson's "Some accounts of the foetus 

 in utero being differently affected by the Small Pox". This was the 

 earliest investigation of the permeability of the placenta to patho- 

 logical agents. "That the foetus", said Watson, "does not always 

 partake of the Infection from its Mother, or the Mother from the 

 Foetus, is the subject of this paper." Two of his cases, he said, "evince 

 that the Child before its Birth, though closely defended from the 

 external Air, and enveloped by Fluids and Membranes of its own, is 

 not secure from the variolous Infection, though its Mother has had 

 the Distemper before. They demonstrate also the very great Subtility 

 of the variolous Effluvia". But other cases "are the very reverse of 

 the former, where though from Inoculation the most minute portion 

 of Lint moisten'd with the variolous Matter and applied to the slightly 

 wounded Skin, is generally sufficient to propagate this Distemper; 

 yet here we see the whole Mass of the Mother's Blood, circulating 

 during the Distemper through the Child, was not sufficient to pro- 

 duce it. . . . From these Histories it appears that the Child before its 

 Birth ought to be consider'd as a separate, distinct Organization; 

 and that though wholly nourish'd by the Mother's Fluids, with 

 regard to the Small Pox, it is liable to be affected in a very different 

 Manner and at a very different Time from its Mother". Doubtless 

 the modern explanation of Watson's discordant results would be that! 

 in one case there were placental lesions, destroying the perfect barrier 

 between the circulations, and in others there were not. 



In the last year of the century (but the seventh of the Republic) 

 Citizens Leveille & Parmentier contributed an interesting paper to I 

 the Journal de Physique in which they observed the increase in size] 

 of the avian yolk on incubation and spoke of a current of water yolk- 

 wards (see Fig. 225). 



3* 15. The Beginning of the Nineteenth Century 



At the beginning of the new century a fresh influence came in! 

 with the work of Lamarck, though it did not have such a great effect 

 on his contemporaries as on later generations. Its relations with] 

 biochemistry are so remote that there is no need to deal in any detail 



