o20 J. T. IRVING AND C. S. HANDELMAN 



but at some distance from the bone. In no case had the giant cells 

 engulfed trypan blue. Almost all the giant cells of diameters up to 

 100 microns had up to 12 nuclei arranged circumferentially around 

 the cell, and very few had less than 6 nuclei. They were usually much 

 larger than osteoclasts found around bone, in which the nuclei are 

 usually more central. The cytoplasm was generally acidophilic, and 

 all the cells were seen tightly applied to bone. The only other for- 

 eign bodies around which they were found were hairs which had 

 accidentallv been introduced. The giant cells were sometimes pres- 

 ent in a long, thin shape, around projecting parts of bone, or else 

 were in typical Howship's lacunae, where they were circular or oval 

 in shape. No intermediate types with 2 or 4 nuclei were convincingly 

 seen. This might be due to the timing procedure adopted, which 

 failed to catch cells at this stage; but it seemed that the appearance 

 of the multinucleated cells was a very sudden process. 



Loss of weight of the implants was evident by 2 weeks, the time 

 at which the giant cells began to appear in significant numbers. 

 Thereafter it proceeded at a constant rate ( Fig. 3 ) . 



The giant cells about the decalcified implants were exceedingly 

 active for all the oxidative enzymes studied, the activity of these 

 cells being equivalent in intensity to that of the osteoclasts of the 

 skeleton of the newborn rat (Figs. 4 to 9). Acid phosphatase ac- 

 tivity was less intense in the giant cells about the implant than 

 that seen in the skeletal osteoclasts (Figs. 10 and 11). In some cases, 

 the giant cells were flattened and difficult to differentiate from the 

 surrounding cells (Fig. 7). When an enzyme process was applied, 

 it became immediately obvious which they were ( Fig. 8 ) . 



Group 2 



The sections of devitalized bone from rachitic animals showed 

 a difi^erent picture from those of group 1. The von Kossa and Gomori 

 techniques showed that calcification of the rachitic osteoid began 

 soon after implantation. By 1 week a few giant cells were seen on 

 calcified surfaces, but they were never seen on osteoid till it calcified 

 (Figs. 12 and 13). As the experiment proceeded, the bone became 

 more heavily calcified and more giant cells were seen attacking it. 



