256 TEXT-BOOK OF PHYSIOLOGY. 



Functions. The functions of the white corpuscles are but imperfectly 

 known, and at present no positive statements can be made. It has been 

 suggested that wherever found in the body, whether in blood or tissues, they 

 are engaged in the removal of more or less insoluble particles of disintegrated 

 tissues, in attacking and destroying more or less effectively various forms of 

 invading bacteria and thus protecting the body against their deleterious 

 activity. This they do by surrounding, enveloping, and incorporating either 

 the tissue particle or bacterium and digesting it. On account of this swallow- 

 ing action these cells were termed by Metchnikoff phagocytes and the process 

 phagocytosis. The cells engaged in this process are the polymorphonuclear 

 leukocytes and the large and the small lymphocytes. He regards them as 

 the general scavengers of the body. It has been suggested that they are 

 also engaged in the absorption of fat from the lymphoid tissue of the intestine. 

 In their dissolution they contribute to the blood-plasma certain protein 

 materials which assist under favorable circumstances in the coagulation 

 of the blood. 



HISTOLOGY OF THE BLOOD -PLATELETS. 



The blood-platelets or plaques are small histologic elements circulating 

 in the blood-plasma. They were discovered and described in 1845 by Arnold. 

 Hayem, later applied to them the term hematoblasts, on the supposition 

 that they were the early stages in the development of the red corpuscles. 

 This is now known to be erroneous. On account of their specific, distinct 

 characters, and their constant presence in the blood of living animals (guinea- 

 pig and bat) , they are now regarded as normal constituents of the blood and 

 designated sometimes as the third corpuscle. When blood is freshly drawn 

 from the body, the plaques rapidly undergo disintegration and disappear; 

 but by treating the blood with osmic acid, the form and structure of the 

 plaque may be retained. They may also be preserved by preparing and 

 staining the tissues with Wright's blood stain. 



The blood-platelet may be defined as a colorless, grayish-white, homo- 

 geneous or finely granular protoplasmic disk, varying in diameter from 1.5 

 to 3.5 micro-millimeters. The edges are rounded and well defined, but it 

 is not certain whether they are only flattened or are slightly biconcave. 

 There is, however, no nucleus, though the central portion is granular and 

 the peripheral portion clear. The ratio of the plaques to the red corpuscles 

 is i to 1 8 or 20, and the total number per cubic millimeter has been estimated 

 to be 250,000 to 300,000 or more. 



When blood is shed they tend to adhere to each other and form irregular 

 masses known as Schultze's granular masses. If threads are suspended in 

 blood, the plaques accumulate in enormous numbers upon them and appear 

 to form a center from which fibrin filaments radiate as coagulation proceeds. 

 The white thrombi which form in blood-vessels in consequence of diseased 

 states e.g., endocarditis, atheromatous ulceration, etc. are composed very 

 largely of blood-plaques and fibrin threads. 



The blood-plaques can be seen with high powers of the microscope in the 

 blood-vessels of the omentum of the guinea-pig and rat, especially when the 

 blood-stream begins to slow. They are also readily seen in the blood-vessels 

 of subcutaneous connective tissue of various animals, and especially in that 



