FOODS HUMAN NUTEITION. 269 



this hacillus could be kept at temperatures of 22° and under for many months, 

 without showing any signs of blowing. If, however, such contaminated tins, 

 although apparently sound when examined in this country, were exposed to a 

 leuu)erature such as is likely to be met with in the Tropics, they would rapidly 

 become decomposed." 



" To ensure complete sterilization, the temperature of the medium surround- 

 ing the tins, must alw^ays be above 112°. The lowest temperature of the sur- 

 rounding Iluid which will completely sterilize the tins, within a reasonable time, 

 is 120°, and this temperature must act for uot less than GO minutes. 



"From the two experiments recorded with a fluid boiling at i;>0°, it would 

 appear that even then at least an hour would be required to ensure the death 

 (.f these very resistant spores. We are aware that the above results do not 

 tally with the usually accepted idea of the thermal death point of spore-bearing 

 bacilli, but we would point out that experiments have not before, to our know- 

 ledge, been made with this particular bacillus. 



"The experiments were carried out with evei*y available precaution against 

 error and repeated often enough to ensure accuracy." 



Report on the nature and causes of the blackening' of the interior of tins, 

 W. AV. O. Bevhriijge (In Third Report of Voiinnittvv on Plufsiolofiicdl Effects of 

 Food, Training, and Clothing on the Soldier. London: Gt. Brit. War Off., 1908, 

 pp. 73-79; Jour. Roy. Army Med. Corps, 13 {1909), No. 3, pp. 326-332).— Experi- 

 mental studies were made with a view to determining the cause of the discolora- 

 tion of the interior surface of tin cans, particularly those containing meat. 



According to the author. " the discoloration of the interior of tins containing 

 moist foods, which have been sterilized by heat, varies from a mere browni stain 

 here and there to complete blackening, and, in cei'tain cases, actual erosion of 

 the metal. 



" The discoloration is insoluble in water, alcohol and ether, and is not vol- 

 atized by heat. It is soluble in mineral acids, and to a large extent by alkalis, 

 such as sodium hydroxid. In many cases some of the greasy discoloration will 

 be found to be soluble in ether, paraffin, or glycerol. From chemical analysis 

 the blackening may be said to be due to : (1 ) Sulphid of tin ; (2) sulphid of iron ; 

 (3) oleate of iron." 



From his investigations he concludes that " except in cases where the contents 

 of the tin are blackened by contact, or w^here there is actual erosion of the metal, 

 the discoloration of the tin is probably not in any way deleterious to the con- 

 sumer, nor has it any injurious effect upon the food itself. 



"Except in the case of bacterial fermentation, a high temperature, above 110° 

 C, appears to be essential. 



" In putrid samples of tinned meats, blackening and erosion of the metal can 

 easily be accounted for by bacterial fermentation, caused by anaerobic spore- 

 bearing bacilli, which forms large quantities of H-S mercaptan bodies and acids, 

 these reacting on the tin form sulphids of the metals. 



" Perfectly fresh meats having an acid reaction may be sterilized at even a 

 high temperature (120 to 130° C.) without causing blackening of the tin. 



" Where alkalinity of the food exists, from being tainted or from having 

 become so during the pickling process, and where the heat of sterilization is 

 carried too far. much blackening of the interior is liable to result. 



"Acidity of the contents, except where it exists in a high degree, does not 

 cause the same amount of discoloration as in the case of foods having an alka- 

 line reaction. 



" Excess of fat, combined with a high degree of heat in the presence of 

 superheated steam, is responsible for a certain amount of discoloration. 



