232 VITAMIN D GROUP 



tion, and it forms a large mass which contril)iites largely to the swelling of 

 the j miction. 



Both the endosteal and periosteal siu'faces of the calcified cortex are 

 covered l)y osteoid tissue. It is most extreme near the epiphysis but extends 

 the entire length of the shaft. At times the osteoid may be so al)inidant as 

 to decrease the diameter of the marrow cavity. The calcified portion of the 

 cortex is considerably reduced in thickness, and in places calcium salts 

 appear to be entirely lacking. 



The blood vessels are not dilated, and hyperemia is not pronounced. 



Bechtel et al} ha\'e given a detailed description of the microscopic changes 

 in the bones of ricketic calves which for the most part agrees with the find- 

 ings of Pappenheimer. 



B. IN PATHOLOGY OF HUMAN BEINGS 

 BENJAMIN KRAMER and ABRAM KANOF 



The pathological changes in human beings resulting from deficiency of 

 vitamin D are almost entirely confined to the skeleton. Here there develops 

 a distortion of bone growth which gives rise to the clinical picture which we 

 designate as rickets. The primary distiu'bance responsible for this distor- 

 tion is a failure to mineralize newly formed osteoid tissue and cartilage 

 matrix. Hence, the unusual softness of the bone which under the stress and 

 strain of weight bearing and locomotion gives rise to the characteristic 

 deformities of the disease. To understand these changes it is important to 

 review the process of normal bone development and growth.^"- ^^ 



From the point of vieAV of embryologic development there are two types 

 of bone. The first is membranous bone, occurring in the vault of the skull, 

 the lower jawbone, and part of the clavicle. The first step in the formation 

 of these bones in the blastoderm is a condensation of the mesodermal cells 

 which soon develop into fibrous membrane. Between the cells of this mem- 

 brane a dense intercellular substance accumulates, and when the proper 

 stage of development of this substance is reached calcium is deposited into 

 it. The property of calcifiability is conferred upon the transformed connec- 

 tive tissue by the osteoblasts. Osteoblasts arise in the early embryo by 

 direct transformation from mesenchymal cells. In the adult they arise from 

 fibroblasts and reticular cells. It is through the activity of these osteoblasts 

 on the fibrous sheath that the bone attains increasing thickness, as addi- 

 tional layers of periosteum are laid down and ossified without the inter- 



8" A. Robinson, Cunningham's Textbook in Anatomy. William Wood and Co., New 



York, 1923. 

 ^'^ A. A. Maximow and W. Bloom, A Textbook of Hist( logy. W. B. Saunders and Co., 



Philadelphia, 1948. 



