HISTOLOGY. 



d.f. 



tissue of pearly luster, containing neither capillary nor lymphatic vessels, 

 nor nerves. In the umbilical cords of young embryos it closely resembles 

 mesenchyma. At birth its cells, which retain their protoplasmic con- 

 nections with one another, appear fusiform (spindle-shaped) or triangular 

 rather than stellate. The intercellular substance consists of fibrils in 

 irregular bundles, embedded in a matrix containing mucus. It has long 

 been debated whether these fibrils originate in the matrix directly, by a 

 sort of precipitation or coagulation, or develop in the outer protoplasm 

 (exoplasm) from which they later become separated. The tendency is 

 toward the latter interpretation. In specimens specially stained, Fig. 40, 

 the protoplasm may present a sharp fibril-like border staining differently 

 from the intercellular fibrils. Chemical changes in the fibrils may occur 

 after they have left the cells. Elastic fibers, to be described under con- 

 nective tissue, are not found in the 

 mucous tissue of the umbilical cord. 



The mucins are a group of com- 

 pound proteid bodies containing a car- 

 bohydrate complex in their molecule 

 and therefore known as glycoproteids. 

 There are many varieties, the mucus 

 of gland cells and of the mucous tissue 

 just described both containing true 

 mucins. Related substances, called 

 mucoidsy have been obtained from ten- 

 don, cartilage and bone. The develop- 

 ment of mucus by connective tissue 

 cells does not produce anything corre- 

 sponding with goblet cells. It is only 

 in connection with other sorts of secretion that connective tissue cells are 

 said to elaborate granules which are converted into vacuoles. 



All embryonic connective tissues are thought to contain mucus, and 

 a variety of tumor (myxoma) is of this type. The peculiar connective 

 tissue of the cornea, to be described in connection with the eye, contains 

 no elastic fibers and is rich in mucin; nevertheless its structure is very 

 different from that of the substance of 1 the umbilical cord, to which the 

 name "mucous tissue" is particularly applicable. 



CONNECTIVE TISSUE. 



Connective tissue is that derivative of mesenchyma which consists of 

 cells either connected with one another or disconnected, and of intercellular 

 spaces largely occupied by fibers of two sorts, white and elastic fibers 



FIG. 40. Mucous TISSUE FROM THE HUMAN 

 UMBILICAL CORD, AT BIRTH. Mallory's 

 connective tissue stain. 



d. f., Dense bundle of fibrils; m., mucus con- 

 taining intercellular substance; 1. f., 

 loose fibrils; c., cell with fibril-like border. 



