PLASMA. 151 



the plates have been shown to be fragments of giant cells they can scarcely 

 be homologous with the amphibian thrombocytes. 



Plasma is the fluid intercellular substance of the blood. It contains 

 various granules some of which are small fat drops received from the 

 thoracic duct. Others occurring in variable quantity are refractive parti- 

 cles, not fatty, either round or elongated; they are known as haemato- 

 konia (or haemokonia). In ordinary sections the plasma appears as a 

 granular coagulum. 



LYMPH. 



The contents of the lymphatic vessels is called lymph. It is a fluid 

 which may contain the various cellular elements of blood in small numbers. 

 Red corpuscles and polymorphonuclear leucocytes are occasional. Lym- 

 phocytes are the most abundant cells, and some of them have considerable 

 protoplasm and are phagocytic. The lymph fluid is not identical with 

 plasma or with tissue fluids, yet all three are similar. Nutrient material 

 from the plasma traverses the tissue fluids to the epithelial cells, certain 

 products of which pass back into the tissue fluids. They may be taken 

 up by the blood or by the lymph, first passing through the endothelial cells 

 of the vessels. From the intestine much of the absorbed fat is transferred 

 across the tissue spaces to the lymphatic vessels in which it forms a milky 

 emulsion known as chyle. (The small lymphatic vessels containing it have 

 been known as lacteals.) This example shows that lymph may exist in 

 more than one form. In the subclavian veins it mingles with the blood 

 plasma. 



In ordinary sections lymph appears as a fine coagulum, containing a 

 few lymphocytes, and occasionally other corpuscles. 



