The original system as developed by Einthoven was too heavy, because of its water cooled electromagnets, to be applied in a clinical setting. Therefore a portable system should be constructed and this was in Europe realized by the French company Boulitte, situated in Paris (1920-1930). Mr. G. Boulitte was one of the first bioengineers. His cardiograph consisted of a light source which throws a shadow of a string which is stretchedin the magnetic field of two electromagnets (forming the string galvanometer) onto a photo sensitive film by means of an optical microscope. Electrodes attached to a patient are connected to the string, which will move due to Lorentz forces, in the rhythm of patients electrical heart activity. The result is an ECG recorded on the film, which becomes visible, after the film has been developed. A metal strip act as a chopper that periodically blocks the light beam to create a time base on the film. The three leads can be selected by means of switches. The instrument company Dr. D.H. Cocheret in Arnhem, well known in the Netherlands for delivering different biomedical instruments, imported the Boulitte electrocardiographs and sold them to most of the Dutch hospitals, where the system was in use from 1930 upto 1950. The creation of the Boulitte electrocardiograph started in fact the specialism clinical cardiology and can as such be considered as one of the first attainments of Technical Medicine. .