MARROW OR MYELOID CELLS. 155 



be detached, when they are fonnd to have the ap- 

 pearance of large compound cells, consisting of many 

 smaller ones. They are met with in numbers beneath 

 the periosteum as well as beneath the medullary 

 membrane These, in fact, represent the early stage 

 of the formation of bone tissue, and ordinarily undergo 

 ossification. In some forms of disease, however, they 

 grow and multiply very rapidly without becoming con- 

 densed or calcined. They may accumulate so as to form 

 a vast amount of soft and rapidly increasing spongy 

 tissue, which has been truly considered to be closely 

 allied to certain forms of cancer. The masses above 

 described vary much in size and form in the healthy 

 state, and from the circumstance of their being 

 found in great number in close proximity with the 

 marrow, they have been termed "myeloid cells." In 

 no structure of this kind do we meet with anything 

 to justify the idea that the lacuna? and canaliculi are 

 stellate cells. Each mass is oval, and usually smooth 

 on the surface. The so-called " myeloid cell " is 

 therefore only a spicule or part of a lamina of bone 

 tissue in its soft state containing numerous masses of 

 bioplasm, with as yet very little intervening formed 

 material, and no calcareous matter. 



216. Of the changes occurring in an Haversian sys- 

 tem of fully formed bone. Many years ago Messrs. 

 Tomes and De Morgan (Phil. Trans., 1853) discovered 

 that some of the Haversian canals of the compact tissue 

 of bone were much larger than others, and that the 

 outline of the larger canals as seen in a thin transverse 

 section of the compact tissue, was uneven. By 

 further examination, these observers succeeded in 

 ascertaining the explanation of this imporiant fact. 

 They demonstrated that the several adjacent Haver- 

 sian rods of bone tissue varied very much in age, 

 and that of those seen in a section, even in adult 

 bone, some had only just been formed, or were 

 in course of formation at the time the bone was 



