I configured the file /etc/network/interfaces with this as follows:
auto eth0 allow-hotplug eth0 iface eth0 inet static address 192.168.1.111 gateway 192.168.1.254 netmask 255.255.255.0 dns-nameservers 188.8.131.52 184.108.40.206
and I disabled the service called : dhcpcd. If I disconnect the ethernet cable and wait a few minutes, the Raspberry goes online with another IP : 192.168.1.86. Why is this happening? I don't have any idea.