*.** 



lu-i L I S R A 



THE DISTRIBUTION OF MITOCHONDRIA IN THE PLACENTA, T*" 







Since mitochondria were discovered by Altmann in 1890, a voluminous litera- 

 ture has accumulated on this subject. Mitochondria have been described in almost 

 every type of animal and plant cell and have been credited with functions varying 

 from the transmission of hereditary characters to differentiation into neurofibrils, 

 muscle fibrils, connective-tissue fibrils, and zymogen granules. Other observers 

 believe that they are concerned in the metabolic processes of the cell. Recently 

 the literature has been ably reviewed by Duesberg (1912) and Cowdry (1918), 

 and therefore no attempt will be made to do so here. 



The only reference to mitochondria in the placenta that we find in this exten- 

 sive literature is a note by De Kervily (1916). This writer states that mitochondria 

 are abundantly present in the Langhans cells of the human placenta throughout 

 gestation. He makes no mention of their occurrence in the syncytium or other 

 placental elements. It was consequently deemed of interest to investigate the 

 mitochondria of the placenta more in detail and in different types of animals. We 

 were guided in our choice by the classification of Grosser (1910), who arranged the 

 placentae of animals in an ascending scale dependent upon the union of the chorion 

 with the uterine wall. Following this classification, we have chosen the pig, cat, 

 guinea-pig, and human, as representing several rather distinct types. 



According to Grosser, the pig represents the simplest type, in which the chorion 

 is merely apposed to the folds of the uterine mucosa, in consequence of which the 

 maternal and fetal blood-vessels remain widely separated. In the cat (Carnivora) 

 the union is more intimate as the result of an invasion of the uterine mucosa and its 

 stroma by the chorion, whereby the fetal ectoderm eventually surrounds the mater- 

 nal blood-vessels, and the distance between the maternal and fetal circulation 

 is greatly reduced. In the guinea-pig (Rodentia), a still more intimate fusion of 

 the chorion with the uterine wall occurs. Here the chorion finally erodes the 

 maternal vessels so that their endothelium disappears and the maternal blood flows 

 through channels completely lined by fetal ectoderm. The barrier between the 

 maternal and fetal blood-streams has been reduced to a single layer of chorionic 

 epithelium and a delicate stroma. In the human, conditions are similar to those in 

 the guinea-pig, although there are marked differences in the finer architecture. 



MATERIAL AND METHODS. 



A series of mature placentae from the pig, cat, guinea-pig, and human were 

 obtained and fixed fresh. Placentae of earlier stages of development in the cat and 

 the guinea-pig were also obtained in order to check up the various types of cells 

 found in these animals. 



Small pieces of the material were fixed either in the acetic-osmic-bichromate 

 mixture, formalin-Zenker mixture of Bensley, or the various formalin-bichromate 

 mixtures of Regaud. The sections were stained by the fuchsin-methyl green 



105 



