Draining people of blood for soldiers

Reguarly the German Red Cross would arrive at Auschwitz and take blood from the prisoners.

Anyone who has ever donated blood is aware how carfully and kindly donors are treated. The maximum that is taken at any one time is a pint or its metric equivalent.

In the German camps they drained the people of blood, people who were already starving.

The blood was then used for transfusions for the soldiers on the front. This pracitce was especially carried out during the battle at Stalingrad.

How can the Germans ever try to use the argument that the Wehrmacht was a 'different animal' than the SS? They were using blood drained from people in places such as Auschwitz, Belsen, Buchenwald, Oranienburg et al.