SECT. XXXVIII. 2. i. OF BLOOD, 36? 



cavities or lacunae formed on that fide of the placenta, which is 

 in contaft with the uterus ; thofe cavities or cells are filled with 

 blood from the maternal arteries, which open into them ; which 

 blood is again taken up by the maternal veins, and is thus per- 

 petually changed. While the terminations of the placental ar- 

 teries and veins are fpread in fine reticulation on the fides of 

 thefe cells. And thus, as the growing fejrus requires greater 

 oxygenation, an apparatus is produced refembling exactly the 

 air-cells of the lungs. 



In cows, and other ruminating animals, the internal fur face 

 of the uterus is unequal like hollow cups, which have been 

 called cotyledons ; and into thefe cavities the prominences of 

 the numerous placentas, with which the fetus of thofe aninnals 

 is furnifhed, are inferred, and ftriclly adhere ; though they may 

 be extracted without effufion of blood Thefe inequalities of 

 the uterus, and the numerous placentas in confequence, feem to 

 be defigned for the purpofe of expanding a greater furface for 

 the terminations of the placental veflels for the purpofe of re- 

 ceiving oxygenation from rhe uterine ones ; as the progeny of 

 this clafs of animals are more completely formed before their 

 nativity, than that of the carnivorous clafles, and mud thence in 

 the latter weeks of pregnancy require greater oxygenation. 

 Thus calves and lambs can walk about in a few minutes after 

 their birth ; while puppies and kittens remain many days with- 

 out opening their eyes. And though on the feparation of the 

 cotyledons of ruminating animals no blood is efFufed, yet this is 

 owing clearly to the greater power of contraction of their ute- 

 rine lacunx or alveoli. See Medical Eflays, Vol V, page 144- 

 And from the fame caufe they are not liable to a fanguiferous 

 menftruation. 



The necefllty of the oxygenation of the blood in the fetus is 

 farther illuftrated by the analogy of the chick in the egg ; which 

 appears to have its blood oxygenated at the extremities of the 

 veflels lurrounding the yolk ; which are fpread on the air-bag 

 at the broad end of the egg, and may abforb oxygene through 

 that moid membrane from the air confined behind it ; and which 

 is (hewn by experiments in the exhausted receiver to be change- 

 able^ through the (hell See Phy'tologia, Sett. III. 



This analogy may even be extended to the growing feeds of 

 vegetables -, which were (hewn by Mr. Scheele to require a reno- 

 vation of the air over the water, in which they were confined. 

 Many vegetable feeds are furrounded with air in their pods or 

 receptacles, as peas, the fruit of itaphylea, and lichnis veficaria 5 

 but it is probable, that thofe feeds after they are flied, as well as 

 the fpawn of filli, by the fituation of the former on or near the 



VOL. I. Z z moift 



