22 THE BLOOD 



the marrow of all the bones is red ; but in the adult, red marrow exists 

 in the cancellated structure of the flat bones only. It has been shown 

 that the red marrow is the most efficient agent in the formation of cor- 

 puscles. In the adult the corpuscles are developed largely in the 

 marrow of the ribs. In this situation, large pale cells make their 

 appearance, which soon become partly colored with hemoglobin. The 

 protoplasm, thus colored, afterward separates into smaller bodies, cup- 

 shaped at first, which eventually take on the characters of the red 

 corpuscles. Mingled with these which may be called mature cor- 

 puscles are smaller bodies, containing hemoglobin, that are capable 

 of ameboid movements. It is probable that red corpuscles are produced 

 from similar cells developed in the liver, spleen, thymus and lymphatic 

 glands, at least in adult animals (see Plate I, showing cells in bone- 

 marrow). 



LEUCOCYTES AND LYMPHOCYTES 



In addition to the red blood-corpuscles, at least five varieties of white 

 corpuscles have been studied and described in the human blood. The 

 .proportion, of these corpuscles to the red varies in different persons and 

 at different times of the day. It is usually as one__to_five hundred^ 

 or about ten thousand in a cubic millimeter. These bodies, which were 

 first described by Hensen, are white, globular and nucleated. 



Leucocytes. The first variety of leucocytes constitutes about 

 seventy-two per cent of the total number. These are described under 

 the name of large polynuclear neutrophiles. They often contain two or 

 more nuclei, and their cytoplasm presents granules that have an affinity 

 for neutral aniline dyes hence their name. They probably are pro- 

 duced largely in the red marrow of bones. They are capable of 

 ameboid movements and of incorporating in their substance and de- 

 stroying foreign particles. For this reason, as well as on account 

 of their great number in the blood, they are regarded as more 

 important than other bodies of a similar nature. It is thought pos- 

 sible that these leucocytes are capable of protecting the organism 

 against pathogenic bacteria, acting as phagocytes. They are consid- 

 erably larger than the red corpuscles, measuring about 2 sVo ^ an ^ nc ^ 

 (10 fji) in diameter. 



The second variety is known as large mononuclear leucocytes. 

 These also are larger than the red blood-corpuscles. They may be 

 polynuclear leucocytes in a transitional condition, the nucleus finally 

 assuming the forms noted in the first variety. The protoplasm sur- 

 rounding the single nucleus in these bodies is clear, and this variety 

 has received the name of myelocytes. They probably are developed 



