CELLS IN CONNECTIVE TISSUE 71 



the blood vessels. They may emigrate from the vessels as plasma cells, or they may 

 be formed from emigrated lymphoid cells. They have been seen in the act of emigra- 

 tion and the shapes of many of the cells in the interstitial tissue can leave no doubt as 

 to their amoeboid character. We are led to the belief that the plasma cells have their 

 origin in the lymphoid cells from the similarity of their nuclei to those of lymphoid cells 

 and from the presence of transitional forms. 



Downey (Folia haemat., 1911, vol. n, pp. 275-314) supplies a useful 

 review of the literature of plasma cells, and expresses his opinion that 

 they arise from several sources. 



Plasma cells are found in connection with chronic inflammation of 

 many sorts. They occur normally in abundance in the mucous membrane 

 of the digestive tube from the stomach to the rectum, and they may be 

 seen in bone marrow and in the lymphoid organs. Occasional plasma 

 cells may be expected in subcutaneous tissue and in the breast. 



Reviewing the preceding paragraphs it is seen that connective tissue 

 contains nbroblasts_or connective tissue cells, and that mast cells, eosino- 

 philic cells, plasma cells and lymphocytes may be lodged in the intercellu- 

 lar spaces. Except the plasma cells, which probably develop from lym- 

 phocytes, these are all comparable with forms of blood corpuscles normally 

 found within the vessels. The source of these corpuscles will be further 

 considered with the blood, together with other forms which sometimes 

 leave the vessels but which are never regarded as constituents of connect- 

 ive tissue. 



In the connective tissue of amphibia and mammals, Ranvier described certain 

 slender branched cells which he named clasmatocytes (Arch. d'Anat. micr., 1900, vol. 3, 

 pp. 122-139). This term refers to the detachment of portions of their processes, which 

 Ranvier believed took place normally as a method of discharging a secretion. The 

 breaking down was observed chiefly in amphibian cells which are now considered to be 

 mast cells. Like other mast cells they are prone to distintegrate. The cells in mam- 

 mals, to which Ranvier referred, are regarded by Maximow as derived from wandering 

 lymphocytes. He believes that these may send out several processes, or become 

 spindle-shaped, thus producing "clasmatocytes," but since this name is inappropriate 

 he calls them resting wandering-cells. He finds that they contain a limited number of 

 vacuoles and coarse granules, but the granules are said to differ from those of mast cells 

 (Arch. f. mikr. Anat., 1906, vol. 67, pp. 680-757). The significance of these cells is 

 uncertain. 



Connective tissue contains two additional types of cells, which are so 

 distinct that they may be regarded as separate tissues. These are the 

 pigment cells and the fat cells; the latter will be described as adipose 

 tissue. 



Pigment cells. The color of the various tissues is due to pigments, 

 which may be involution, like the haemoglobin in red blood corpuscles and 

 the lipochromes in fat; or they may occur as granules imbedded in the 

 protoplasm. The granules, which are yellow, brown, or black, often 



