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 8.8.4.4 8.8.4.4
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.