The term “offal” in its application to meat residues is somewhat ambiguous. It not only comprises material coinciding with the general interpretation of the term, but certain portions of the animal which are really suited to the preparation of foodstuffs for the table. Consequently all grease recovered from the digester is not necessarily adapted to manufacturing purposes only. In these circumstances it is necessary to grade the fat before treatment, the fresh fat, which is quite suitable for yielding material adapted to the preparation of margarine, for instance, being kept distinct from the lower grades which cannot possibly be classed as edible. Selection and separation treatment of the two grades--edible and inedible--are profitable because, while both are in keen demand, it is the former which is able to command the higher market figure. But when edible fats are sought it is preferable to employ the steam-jacketed digester because the fat thus obtained, from the fact that the steam is not brought into contact with the material during the cooking process, is of enhanced quality, being sweeter, while all the natural properties of the fat are retained for reasons already set forth. Although, therefore, the most popular system in vogue for reclaiming fat from slaughter-house residues is exposed to criticism, owing to what may be described as lack of efficiency in operation due to the recovery of the fat not being as high as it might be, it appears to meet the conditions of the average municipal abattoir. City and borough corporations, unlike private organizations, are not in the position to scrap an existing plant for one which is of later date and greater efficiency, because there is not the same incentive to reap the utmost benefits attainable as prevails under private conditions where the full brunt of competition is encountered. Of course, the initiative of corporations is just as pronounced as that of private firms and individuals, but it is the exception rather than the rule. Furthermore, the municipality is not in the position to run a plant under full load, or even at a uniform pressure the whole time. It is only able to handle the waste as it accumulates during its own abattoir operations. On the other hand, the private exploiter can acquire a plant of such capacity as to cope with the steady flow of material from the slaughter-houses, thereby keeping the by-product recovery installation working steadily at a point approaching its productive limits.