Abstract: Process for modifying an existing breast box for a paper or cartonmaking machine as well as an intermediate portion for carrying out the process. During the fabrication of a breast box for a paper or cartonmaking machine an intermediate portion is interposed between a supply apparatus and a downstream guiding device, with the material suspension flowing through this intermediate portion wherein, via supply lines, located on the intermediate portion, a liquid is added which differs from that of the suspension stream. Particularly, in this manner, already existing breast boxes can be converted, to water dilution technology, with this invention setting forth special embodiments of differing intermediate portions that can be utilized therefor.