DISTRIBUTION OF MITOCHONDRIA IN THE PLACENTA. 113 



The cells representing the remains of the Langhans layer lie just beneath the 

 syncytium. They are usually seen in groups of 2 to 4 cells, though many isolated 

 cells are present and occasional groups of 10 to 15 cells can be found. Many of 

 these cells are senile and have vacuolated protoplasm and pycnotic nuclei. Others 

 appear to be quite healthy and normal. They range from 10 to 20 /u in greatest 

 diameter and vary in shape from isolated oval or spindle cells to rows of low 

 cuboidal cells. The nucleus is rather large, stains light green, and contains 1 to 4 

 medium-sized basophilic nucleoli and a delicate chromatin network. 



The protoplasm is clear and unstained and contains a moderate number of 

 mitochondria. These are usually small, irregularly curved rods of moderate length, 

 and many of them have small nodules at their extremities. A few granular forms 

 are present. The mitochondria are sharply differentiated in the clear unstained 

 protoplasm and this enables one to recognize these cells, regardless of their form or 

 position. As the signs of degeneration increase the mitochondria decrease in number 

 and size. No vesicles or other granules are seen in these cells. The Langhans cells 

 are easily found in all mature human placentae. 



The decidual cells are found in an irregular layer next to the uterine wall as 

 short columns projecting into the labyrinth. They are large round to oval cells 10 

 to 30 M m diameter, and resemble somewhat the giant cells found in the placentae 

 of the pig and the cat, although they are entirely different in origin. They contain 

 one or two large round or 1 oval nuclei which stain a faint green and contain in turn 

 one or two large basophilic nucleoli and a delicate chromatin network. 



The protoplasm stains more intensely than the nucleus and is quite rich in 

 minute mitochondria. They are in the form of short rods and granules and are 

 distributed uniformly through the protoplasm. The protoplasm of many of these 

 cells contains a colloid-like substance which stains deeply with fuchsin. It varies 

 in amount from a few small droplets to large irregular masses 4 to 5 M in diameter. 

 An apparently normal cell may contain a large amount of this substance and the 

 surrounding cells be entirely free from it. It is not present in the degenerating 

 cells. Decidual cells are present in all stages of degeneration. 



As senility advances, the nucleus becomes homogeneous and stains deep green, 

 the protoplasm loses its affinity for the green, and the mitochondria decrease in 

 number and size and finally disappear entirely. 



CONCLUSION. 



From the foregoing description, it will be seen that mitochondria are abundantly 

 present in the various types of placentae investigated. They are particularly numer- 

 ous in those cells which form the barriers between the maternal and fetal circulation 

 and through which the respiratory and nutrient interchange between the two 

 organisms is constantly proceeding. 



To review briefly, in the pig, mitochondria are very plentiful in the layers of 

 epithelial cells, namely the chorionic ectoderm and the uterine mucosa which form 

 the bridge between the maternal and fetal blood-streams. They are also found in 

 great abundance in the epithelium of the uterine glands and this is significant, 



