FCETAL NUTRITION: THE PLACENTA 



437 



significance 



are 

 uvanules 



unknown. Besides tlie 

 and fat, otlicrs are filled 



but its composition and 

 leucocytes that contain pigment 

 with rod-like bodies, the 

 " Uterinstiibchen " of Bonnet.^ 

 Later they appear in the uteiine 

 milk. Rods have also been de- 

 scribed in the trophoblast of 

 the raljljit by Beneden, and 

 in the uterine mucosa by 

 .Schniidt,^ who stated that they 

 were composed of calcium oxa- 

 late. In Ruminants they ai'e 

 found in enormous numljers, but 

 whether they form a supply of 

 calcium for the fretus is not 

 known (Fig. 121). There is at 

 present no evidence that they 

 are "protein crystals," a name 

 sometimes applied to them.-' 



' Bonnet, "Beitriige zur Embryo- 

 logie der Wiederkiiuer gewonnen am 

 Schafe," Airh. f. Anal. v. I'/ii/s., Anat. 

 Aljth., 1884. 



'' (Quoted by Bonnet, " Ueber Em- 

 bryotrophe," J/(«(cA. vjierY. Hoc//., 1899. 



^ Jenkinson (Vertebmti/ Emliri/o- 

 /ogi/, London, 1913) has described 

 " the curious, rounded or elongated, 

 often flattened, bodies, sometimes 

 soft, .sometimes hai-d and brittle, 

 found floating in the allantoic fluid, 

 and familiar for many centuries 

 under the title of 'hippomanes.' In 

 the cow they are white or pale 

 yellow, in the sheep a dirty brown. 

 In the sheep they are formed by 

 local accumulations of the viscid 

 uterine milk, which get into pockets 

 of the. trophoblast between the 

 cotyledons. Gradually, pushing the 

 trophoblast and allantois in front of 

 them, they make their way int(j the 

 cavity of the latter, in which they 

 lie attached by a stalk to the wall ; 

 the stalk narrows and breaks, and 

 they are free in the cavity. At first 

 they aie suii'ounded by a membiane 



— the i-emains of their covering of allantois and trophoblast — and are soft ; they 

 are composed of granular coagulable material, full of cell-detritus, degenerating 

 nuclei, globules of fat and glycogen, and leucocytes. Later the membrane 

 disappears, and the bodies become hard by being saturated with calcium oxalate 

 in the form of 'envelope' crystals. In the cow, when outside the choiion and 

 still soft, they are a bright orange colour, due to the presence of bilirubin, 

 doubtless derived from the extravasated corpuscles eaten by the trophoblast ; 



Fig. 119. — First stage of cellular secre- 

 tion in the placenta of the cow. 

 Invagination of glandular epithe- 

 lium and some of the underlying 

 connective tissue. (Fi'oni Kolstei', 

 " Die Embiyotrophe placentarer 

 Sanger," ^limt. Hefte, vols, xviii. and 

 xix., 1902-03.) 



