FCETAL NUTRITION: THE PLACENTA 



437 



but its composition and significance are unknown. Besides the 

 leucocytes that contain pigment granules and fat, others are filled 

 with r'od-like bodies, the 

 " Uterinstabchen " of Bonnet. 1 

 Later they appear in the uterine 

 milk. Rods have also been de- 

 scribed in the trophoblast of 

 the rabbit by Beneden, and 

 in the uterine mucosa by 

 Schmidt, 2 who stated that they 

 were composed of calcium oxa- 

 late. In Ruminants they are 

 found in enormous numbers, but 

 whether they form a supply of 

 calcium for the foetus is not 

 known (Fig. 121). There is at 

 present no evidence that they 

 are "protein crystals," a name 

 sometimes applied to them. 3 



1 Bonnet, "Beitra'ge zur Embryo- 

 logie der Wiederkauer gewonnen am 

 Schafe," Arch.f. Anat. u. Phys., Anat. 

 Abth., 1884. 



2 Quoted by Bonnet, " Ueber Em- 

 bryotrophe," Munch, med. Woc/i., 1899. 



3 Jenkinson ( Vertebrate Embryo- 

 logy, London, 1913) has described 

 " the curious, rounded or elongated, 

 often flattened, bodies, sometimes 

 soft, sometimes hard 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 into 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 are surrounded by a membrane 



the remains 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 chorion 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. (From Kolster, 

 " Die Embryotrophe placentarer 

 Sa'uger," Anat. Jfefte, vols. xviii. and 

 xix., 1902-03.) 



