THE CONNECTIVE SUBSTANCE GEOUP. 95 



for the rather remarkable proposition that compact bone is 

 formed out of spongy, and spongy out of compact. 



These marrow channels are a series of branching and anasto- 

 mosing tubes, rich in corpuscular elements and vessels. In 

 young bone the latter are known as red marrow. When a 

 longitudinal section has been made through a tubular bone, it 

 will be seen that the channels are enclosed in an osseous net- 

 work, whose meshes differ much in shape. In the articular 

 extremities they are long and narrow ; at other points, more 

 nearly quadrilateral. 



There is a second variety of marrow, known as yellow, which 

 is found in the central cavity of the long bones. The yellow 

 color is due to the presence of fat, though it also contains 

 peculiar, small, colorless corpuscles, not unlike the leucocytes 

 of the blood, and known as marrow-cells, together with the 

 ordinary branched and nucleated connective-tissue corpuscles, 

 also large multi-nucleated bodies that are usually granular and 

 sometimes striated, and blood-vessels. The large corpuscles 

 are the myeloplaxes of Robin (giant-cells). 



The red marrow also contains marrow-cells, though but few 

 fat-cells. It is remarkable for being the seat of the peculiar 

 nucleated blood-corpuscles that have been described by Neu- 

 mann and Bizzozero. They are transitional between the white 

 and the red in size, and have a uniform yellowish green color 

 (Klein). 



The authors above referred to found the nucleated corpuscles in the red 

 marrow of the ribs and bodies of the vertebra ; they resembled blood-corpus- 

 cles that are found in the human embryo, and were regarded as evidence that 

 the bones have bloodmaking properties. Later researches (Orth and Litten) 

 have seemed to corroborate these views, and to have shown that in certain 

 morbid states of the blood, as in carcinoma, phthisis, and syphilis, an effort of 

 this kind is made for the relief of the constitutional infection. Experiments 

 upon dogs have also added further testimony and have shown that after extreme 

 artificial anaemia there is a new formation of blood-globules, in which the 

 nucleated bodies play an active part, together with other elements, such as the 

 giant-corpuscles of Hayem, etc. These views, however, have met with opposi- 

 tion, and Eutherford (" Pract. Histology," p. 88) maintains that the nucleated 

 corpuscle is an indication of corpuscular disintegration rather than of new- 

 formation. 



The periosteum is a layer of dense fibrous tissue closely 

 covering the bone, and connected with it by a thinner layer of 



