Albert Von Schrenck-Notzing (1862-1929) was a German physician who did a great deal of research into the paranormal, particularly physical mediumship. His book, "Phenomena of materialization" was published in 1920 (which can be viewed by clicking the link).
Albert Von Schrenck-Notzing is said to have found in the course of his investigations that ectoplasm is composed of white or colorless blood cells called leucocytes, which are extracted from the body of the physical medium during materialization.
Von Schrenck investigated a number of mediums including Eva Carreire, Willi & Rudi Shneider and Stanislawa P.
The following photographs taken of polish medium Stanislawa P by Albert Von Schrenck-Notzing show the medium demonstrating the emission of ectoplasm- even through netting which was placed over her head to prevent trickery in the form of regurgitating materials through her mouth.
25 January 1913
23 June 1913
Ectoplasm caught on film for the first time
The medium was still able to produce ectoplasm even with the netting over her head.
This film is apparently today archived at the University of Freiburg at the institute of Parapsychology.