A BIOLOGICAL PHENOMENON 63 



valleys converge gives birth to islets. These islets are called 

 spontaneous grafts. 



When part of a cicatrizing wound is covered by a sheet of 

 sterile filter paper, it can be observed that epithelization 

 progresses more rapidly where the cells have been protected 

 by the sheet of paper. This experiment is not in contradiction 



FIG. 10. INFLUENCE OF MECHANICAL PROTECTION 

 ON EPITHELIZATION 



with the complete inhibition due to the application of cello- 

 phane over the entire wound mentioned above. In the first 

 case, the period of contraction had not begun and the cello- 

 phane was impermeable, whereas in the second, the period 

 of epidermization has already started and fiJter paper is not 

 impermeable. It acts only as a local protection. (Fig. 10.) 



FIG. II. INFLUENCE OF INFECTION 



On the other hand, the following experiment shows the 

 retarding action of infection (Fig. 11). A wound was cicatrizing 

 normally. When it had attained the dimensions of B, Fig. 11, 

 it was observed that there was a point of infection in a corner 

 of the new epithelial tissue at a. The wound was not sterilized. 

 A few days later, it assumed the aspect shown in C, Fig. 11. 



