THE BLOOD AND THE LYMPH 267 



or small mononuclear leukocytes, as their name implies, are the variety 

 found largely in the lymphatic vessels and lymph-nodes. They are 

 spherical, small cells each with only a thin layer of cytoplasm about the 

 large nucleus. They ordinarily show little spontaneous movement, 

 but \Masson and Sepp found that by heating them to 44 or by treating 

 them with placental tissue, peptone, or farina, they began to creep 

 with ameboid movements as do the other sorts of leukocytes. About one- 

 quarter of all the leukocytes to be found in the normal blood are (Ehrlich) 

 of this simple variety. These originate in adenoid tissue lymph-nodes, 

 spleen, etc. The large mononuclear leukpcyte is similar to the preceding 

 sort, except that the cytoplasm is abundant instead of scanty, while the 

 nucleus shows more irregularity in form and structure. These may 



FIG. 140 



Section of a lymph-node: a, fibrous coat which penetrates the organ in the form of trabeculao;. 

 6, lymph-corpuscle; c, trabeculae containing blood-vessels; d, is placed in the medulla of the 

 organ in which will be seen numerous lymph-cords. (Bates.) 



come from the bone-marrow or if not probably they are endothelial 

 cells loosened and floating in the blood. The polymorphonudear 

 leukocytes are well described by their name, for they have nuclei of very 

 various shapes, that of a sausage or horseshoe being perhaps the 

 most common. In these the different parts of the nucleus may be con- 

 nected only by slender bands or even threads of nucleoplasm. The 

 cytoplasm is large and contains fine granules. These are largely neutro- 

 philic in their stain-affinity, but some of them are the "eosinophiles." 

 These are the bone-marrow's specific cells. The basophilic leukocytes 

 are the mast-cells. These are much like the preceding, but some of them 

 have several small nuclei instead of one large and segmented nucleus- 

 They also probably originate in the bone-marrow. 



