THE BLOOD 259 



cytes which take their origin entirely from the lymph-adenoid tissues of the 

 body, e.g., the lymph-glands, solitary and agminated follicles of the intes- 

 tines, etc. As the lymph flows through these structures the lymph-corpus- 

 cles, as the future lymphocytes of the blood are called in these situations, are 

 washed out and carried by way of the lymph-stream into the general 

 circulation. 



In the second group are the transitional forms, the polymorphonuclear, 

 eosinophile and basophile leukocytes which originate from the bone-marrow 

 only. The immediate ancestors of these cells are known as myelocytes and 

 are normally found in the red bone-marrow. These cells, through transi- 

 tional stages, assume the characteristics of the leukocytes just mentioned and 

 pass directly into the capillaries of the marrow whence they are distributed 

 throughout the body. 



Several attempts have been made by different investigators to trace all 

 varieties of leukocytes to a common mother cell. While this is believed to 

 take place during embryonal life, the proofs of such an origin of leukocytes in 

 the normal adult are insufficient and unconvincing. 



After an unknown period of life the leukocytes undergo dissolution and 

 disappear. 



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. In their capacity as phagocytes it has been assumed that 

 they are made more or less efficient by the presence in the plasma of an 

 agent or agents which in some unknown manner render the bacteria less 

 resisting and thus make them more susceptible to the attacks of the leuko- 

 cytes. These agents which are supposed to be secreted by the tissue cells 

 are termed opsonins, from their supposed function, that of preparing the 

 bacteria for leukocytic digestion. 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 sug- 

 gested that they are also engaged in the absorption of fat from the lym- 

 phoid 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 b 7 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- 



