F(ETAL NUTRITION: THE PLACENTA 403 



Mammals a greater or less amount of maternal blood is in direct 

 contact with the trophoblast. In the pig and mare it is re- 

 stricted to individual red blood corpuscles, which find their way 

 to the surface and mingle with the gland secretion. In the ass 

 Strajil ^ has found blood in greater amount, forming small 

 effusions. In the sheep its presence has often been noted by 

 Tafani,^ Bonnet,^ and others. The position of the extravasa- 

 tions in the placenta has been already referred to (see p. 398). 

 In the cow they are apparently not a constant phenomenon, 

 the supply being often restricted, as in the mare, to a few single 

 erythrocytes. In the deer, blood is effused into the glands, 

 but no extravasations take place in the cotyledons. Here the 

 whole of the maternal part of the burr appears to be digested 

 and absorbed by the trophoblast. The greater activity of the 

 foetal ectoderm in the deer is also shown by the destruction 

 of the epithehum over the whole surface of the uterus (Strahl *). 



In addition to blood, the uterine milk contains fat in large 

 quantities. Before pregnancy it may be demonstrated in the 

 sub-epithehal leucocytes which later migrate to the surface. 

 Fat globules are also contained in large amount in the epithehal 

 cells of the surface and glands. According to Bonnet, it cannot 

 be considered as a fatty degeneration because the cells are 

 otherwise healthy ; it is rather a fatty infiltration, the epithelium 

 secreting it from th'e lymph or blood-plasma, storing it and later 

 giving it off to the uterine milk. 



Kolster ^ has described a process by means of which cellular 

 elements are added to the " Embryo trophe." * The gland 



^ Strahl, see Hertwig'a Handb. d. vergl. u. exp. Entwickelungsg. d. 

 Wirbelthiere, 1902. 



^ Tafani, " SuUe Condizioni utero-placentari della Vita Fetale," Arch, 

 della Sciwla d'Anat.-Path., Firenze, 1886. 



' Bonnet, "Ueber Embryotrophe," Deut, Med. Woch., 1899. 



* Strahl, "Ueber die Semiplacenta multiplex von Cervus elaphus " Anat. 

 Hefie, H. xciii., 1906. 



5 Kolster, " Die Embryotrophe plaoentarer Sanger," &c., Anat. Hefte, 

 vols, xviii. and xix., 1902 and 1903. 



° Objections have been raised to the term "uterine milk" because the 

 fluid contains cellular elements, pigment granules, &c., which are not present 

 in the mammary secretion. Bonnet and his follovfers have employed the 

 convenient term "Embryotrophe," but it must be noted that in the sheep 

 it forms the nutriment long after the embryonic stage of the developing 

 ovum is past. The two terms are used indiscriminately in this chapter. 



