874 PHAGOCYTES AND PHAGOCYTOSIS IN IMMUNITY 



make their way through some unknown chemotactic influence into the blood stream. 

 The mode by which their numbers is regulated is unknown. The nucleus usually 

 shows three lobes, but apparently, as the result of aging, these increase to four, five, or 

 six. According to Arneth, these changes can be taken as an index of marrow activity. 

 There is much cytoplasm filled with fine neutrophile granules. These cells are actively 

 motile, highly chemotactic, and play the most important part in the phagocytosis of 

 many bacterial parasites. When foreign proteins are injected into the blood stream, 

 there is first a leukopenia, followed by a leukocytosis in which these cells predominate. 



b) The eosinophile leukocyte. — The parents of this cell are myelocytes. The large 

 round granules have an affinity for acid dyes. Ordinarily they are present in the cir- 

 culation as 1-2 per cent of the whites but may reach a concentration of 50 per cent or 

 more when the host is infected with animal parasites (e.g., Filaria). They emigrate 

 from the vessels and collect about the site of attachment of worms in great numbers. 

 They are also called forth in response to local or general anaphylactic shock — occur 

 in all "sensitivity" conditions, e.g., asthma, sensitization sinusitis, mucous colitis, 

 and in various inflammations of the skin, pemphigus, urticaria, dermatitis herpeti- 

 formis, etc. The nature of the substances which call them forth is unknown, but they 

 are probably certain products of autolysis derived from tissues or from parasites. 

 These cells are concerned but little in the phagocytosis of bacteria under natural condi- 

 tions but may be made to take them up in in vitro experiments (Weinberg and Seguin) .' 



c) The mast cell. — The mast cells are the least understood. They are granulo- 

 cytes which develop late and remain extravascular, since the mast cells of the blood 

 have been shown by Weidenreich to be degenerating cells and not true mast cells. Mast 

 cells occur in the bone marrow, along blood vessels, and between muscle fibers. Their 

 function is totally unknown. 



3. The third strain, the lymphocyte. — This is the last to develop, but its embryol- 

 ogy is uncertain. Originating by mitosis in the lymphoblasts of the germinal centers 

 of the lymph glands, it is widely distributed. It occurs in lymph glands, hemal 

 glands, and spleen, i.e., in a reticulum near lymphatic or vascular sinuses by means 

 of which it enters the blood stream. It also occurs in small follicles near lymphatic cap- 

 illaries and ducts or even in small clumps without such relation, very widely distributed 

 throughout the organs and in bone marrow as well. Thus it may occur wherever there 

 is reticulum. There are smaller and larger lymphocytes. These have the same type 

 of nucleus. In the larger one the nucleus is surrounded by more cytoplasm of less 

 basophilic character and usually contains some coarse granules. More lymphocytes 

 enter the circulation in twenty-four hours than are present at any one time, and in 

 investigating their fate Bunting and Huston found that they made their way on to the 

 mucous membranes, in particular the intestinal mucosa. Why they do this is not 

 known. They are said to be devoid of autolytic and peptic ferments; are extremely 

 sensitive to X-rays and radium; and apparently have some specific relationship to 

 immunity against tumors as shown by the work of Murphy and his co-workers. - 



' Weinberg, M., and Seguin, P.: Compt. rend. Soc. de hiol., 75, 170. 1913. 

 2 Murphy, J. B., el at.: J. Exper. Med., 191 2-21. 



