PLACENTA. 1:3 



and care is taken not to sever the attachment of the placenta to the uterus. Harden the 

 uterus, placenta, and attached foetus, which is still within the amniotic cavity, in the chromic 

 acid and spirit mixture for two weeks, and then transfer them to dilute spirit, and afterwards 

 to strong spirit. The fcetus can be used for making sections of various organs. Make vertical 

 sections through the uterus and the placenta, and stain them with logwood or picrocarmine. 

 and mount them in dammar or Farrant's solution. 



EXAMINATION (L). Observe the uterus, with the placenta lying internal, and firmly 

 attached to it. The placenta consists of a narrow maternal part next the uterus, and a much 

 thicker part the fcetal portion. In the uterus numerous sections of the enlarged uterine 

 sinuses are seen. The fcetal portion consists of richly branched villi, which are separated 

 from each other by a relatively small amount of delicate connective tissue, and a layer of cells, 

 which covers each villus. Within these villi note the loops of blood-vessels. Their distribu- 

 tion is easily seen, because they still contain the coloured blood -corpuscles. 



FRESH HUMAN PLACENTA. 

 PREPARATION. Tease a small piece of a perfectly fresh placenta in salt solution. 



EXAMINATION (L). Observe the large number of isolated and richly branched placental 

 villi. Each one contains a blood-vessel, whose course is easily seen, because it is still filled 

 with blood-corpuscles. A capillary loop is sent into each of the secondary branches on the 

 villus. The villus is covered by a layer of epithelium, whose nuclei are easily revealed by 

 staining the section with magenta solution. This epithelial covering varies in thickness on 

 the same villus. A delicate mucous tissue exists around the blood-vessels. (Indicate the shape 

 and general characters of the villi in PI. XXX., Fig. 3.) 



(H). Observe the capillary blood-vessels filled with blood-corpuscles, and between the 

 vessels note the corpuscles of the mucous tissue which supports them. Study the epithelial 

 covering. It is low, columnar epithelium, with here and there masses of protoplasm, which 

 contain many nuclei. (Indicate the epithelial covering and blood-vessels in PI. XXX., Fig. 4.) 



HOW TO PRESERVE THE HUMAN PLACENTA. 



(1) Osmic Acid. A small piece of the fresh placenta may be teased in a one per cent, 

 solution of osmic acid, and mounted in glycerine. 



(2) Dilute Alcohol. Maceration for forty-eight hours in this fluid is an excellent means of 

 isolating the villi. They may be stained with picrocarmine. 



(3) Miiller's Fluid. Harden very small pieces of a perfectly fresh placenta for three weeks 

 in this fluid. Make vertical sections, and treat them as directed for the placenta of a 

 guinea-pig. 



R 2 



