THE MICROSCOPE IN ANIMAL HISTOLOGY. 189 



tractility, in the healthy body, and in greater numbers in 

 diseased states ; in some cases re-entering the lymphatic 

 circulation, and in others penetrating into various tissues. 

 The pus-corpuscles appearing in the vicinity of inflamed 

 parts are shown by this discovery, made by Waller and 

 Cohnheim, to be nothing but migratory lymphoid or 

 white cells of the blood. The change of form and place 

 of these amoeboid cells is readily seen by placing a drop of 

 frog's blood on a glass cover, and inverting it over a moist 

 cell. As it coagulates, a zone of serum extends round the 

 clot, in which the migrated cells will be found. 



The colorless cells originate in the chyle and lymph- 

 systems, although some may come from the spleen and 

 the medulla of bones, multiplying in the blood itself, and 

 they pass into red corpuscles. Transitional forms have 

 been found in the general mass of blood, in the spleen, and 

 in the marrow of bones. 



The white or colorless cells of blood are identical with 

 the cells of chyle, lymph, pus, mucus, and saliva. They 

 are often described under the term leucocytes (white cells.) 



The leucocytes of saliva (salivary corpuscles) and of pus 

 contain granules or globules of formed material, which 

 exhibit for some time a peculiar dancing movement (see 

 page 120). 



When at rest, or in a lifeless condition, the white cells 

 are of spheroidal form, and generally exhibit granules and 

 globules of fat. Acetic acid develops a nucleus, and some- 

 times splits it into several (Plate XVIII, Fig. 140). 



II. Lymph and Chyle. 



The vessels of the lymphatic or absorbent system re- 

 ceive the liquid part of the blood which has passed from 

 the capillaries, together with the products of decomposi- 

 tion in the tissues, and return them to the circulation. 

 The lymphatics of the intestinal canal receive during 



