178 The Vertebrate Organ Systems 



actions : the eosinophils which stain in the acid stain, eosin ; the neu- 

 trophils which stain in a neutral medium ; and the basophils which stain 

 in a basic medium. All three of these are also called granular leuco- 

 cytes as their cytoplasm appears granular. The neutrophils also are 

 known as the polymorphonuclears due to their possession of a lobated 

 nucleus. The other two main classes of leucocytes are the lymphocytes 

 with their nongranular cytoplasm and large nuclei ; and the monocytes, 

 large cells with eccentric nuclei. 



White blood cells are produced in a number of different tissues 

 throughout the body. These tissues include yellow bone marrow and 

 lymphatic tissues which are scattered in various places, notably the 

 spleen, the lymph nodes, the tonsils, and the mesenteries. 



The platelets are the third of the formed elements in the blood. 

 They are extremely small (0.003 mm. in diameter) and are concerned 

 with the important phenomenom of clotting. The number has been vari- 

 ously estimated as between 250,000 and 500,000 per cubic millimeter of 

 blood. Their place of origin is unknown, but is possibly the bone 

 marrow. 



Since various pathological conditions cause changes in the different 

 blood constituents, blood analysis and study is an important part of 

 clinical procedure. One of the first things usually done is to count 

 the various types of blood cells. A reduced number of red blood cells 

 may indicate a condition such an anemia. An abnormally high number 

 of white blood cells indicates that there is an infection in the body. 

 The different types of white blood cells increase, depending upon the 

 type of infection. A tapeworm infection, for example, results in an 

 increased eosinophil count ; appendicitis increases the neutrophil count. 



The Liquid Portion of the Blood. — The liquid portion of the 

 blood is the plasma. It is the straw-colored liquid that separates from 

 the formed elements when whole blood which has been treated to 

 prevent clotting is allowed to stand. Ninety per cent of the plasma is 

 water; the remaining 10 per cent consists of dissolved solids. Some 

 of the materials carried in the plasma are the soluble end products of 

 digestion (fatty acids, simple sugars, and amino acids), the hormones, 

 inorganic salts, antibodies, blood proteins, metabolic wastes, nitro- 

 geneous wastes, and some blood gases. 



Undoubtedly there are other materials within the plasma, many 

 of whose functions are quite unknown. In spite of the fact that the 

 plasma does contain such a large number of different materials, it 



