Due to their handy appearance, these cards could be reproduced at will and therefore played an exceptional part in the dissemination of portraits amongst scientists. Packed in small envelopes, they could easily be sent around the world by ship, carriage or train. However, cartes de visite were also exchanged in direct encounters, for example, amongst scientists at conferences. For the students, the pictures of their professors were a popular collectible and barter object. For advertising purposes, the back of the card often contained a reference to the photo studio that took the respective photo.