92 G. Marotti, F. Marotti: Topographic-Quantitative Study of Bone Tissue Formation 



denervation. In groups of dogs operated at the same age, the reduction of bone tissue 

 appears, in general, to be more marked in subjects sacrificed 60 and 180 days after 

 limb immobilisation. Obviously, two concurrent factors play a part in this reduction 

 in the growing animals: namely, a decrease in appositional growth in the shaft and 

 an increase in resorption which is not fully compensated by deposition of newly 

 formed bone. 



2. A relatively greater amount of osseous tissue is laid down in the mert than m 

 the contralateral mobile bones during the period of acromycin administration. This 

 is more marked in the two dogs operated upon in adult life: the relative amount of 

 newly formed osseous tissue Is from 5 to 20 times greater in the inactive than in the 

 mobile bones in these subjects (Fig. 2, right). In the two dogs sacrificed 20 days after 

 operation, such a difference in osteogenic activity in the inactive compared with the 

 control mobile bones was not observed (Fig. 1; Fig. 2, left). 



3. The amount of bone tissue undergoing reconstruction in the inert as well as In 

 the mobile bones varies in different long bones In each subject: relatively it is smaller 

 in the humerus and much greater in the ulna. 



The percentage values of the ratio of newly apposed acromycin labelled bone to 

 the total bone, estimated on an entire cross section at the middle level of the proximal 

 metaphysis of the humerus (H.), radius (R.) and ulna (U.) of the inert and mobile 



7o 

 W- 



35 ^ 



30- 



25- 



20- 



15 



I I right (con fro/) 



Mx 13 

 Mn J.I 



Mx 3 1 

 Mn 2.3 



26 25 33 

 H. R. U. 

 A ffer 20 days 



55 V7 70 



H. R. U. 

 After eodays 



35 



20- 



I I riq/it (control) 

 n2 left 



Mx 19 J 

 Mn 55 



din 



H. R a 



After 60 da\js 



Mx 5.6 



Mn ^.7 



n \v^ 



52 53 6S 

 H. R. U. 

 After J6(7days 



F,g. 4 



limbs of all the dogs studied are shown In Fig. 3 (operation at 2-month old) and in 

 Fig. 4 {left, operation at 4-month of age; right, operation at 3 years of age). 



The results obtained at the level of the metaphysis are similar to those of the same 

 bones at the mid-shaft level. However, bone turnover, during the period of aero- 



