INFLUENCE OF VACUUM UPON GROWTH OF BACTERIA 299 



tive, but not enough to be of practical importance. This table 

 also shows the influence of the amount of acid, and also the fact 

 that B. mesentericus is somewhat more easily destroyed by heat 

 than B. subtilis. 



SUMMARY 



From the results obtained, we are inclined to believe that 

 B. mesentericus predominates in canned foods because it is capable 

 of growing to some extent in absence of air, rather than because 

 its spores are more heat resistant than some other types of 

 aerobic bacteria. 



The amount of vacuum under which spores of these organisms 

 are placed during the heating does not influence the thermal 

 death point. 



The small amount of acid present had but slight retarding 

 influence upon the growth of these organisms in air, but did have 

 a marked influence upon the thermal death point. It may be 

 that the beneficial influence of acid upon the keeping of canned 

 foods is due more to the lowering of the thermal death point than 

 to the inhibition of growth of the organisms. 



The amount of air remaining above the Uquid has little in- 

 fluence upon the growth of these bacteria, since sealing the tubes 

 prevents all but minimum growth. This inhibiting influence is 

 more marked in case of B. subtilis than in case of B. mesentericus. 



REFERENCES 



Bitting, A. W., axd Bitting, K. G. 1916 Canning and how to use canned 



foods. Bull. 14, National Canners Assoc, Washington, D. C, 191 pp. 

 Bruett, E. M. 1919 Utility of blanching in food canning. Effect of cold shock 



upon the bacterial death rates. Journ. of Ind. & Eng. Chem. 11, 



37-39. 

 Bdshnell, L. D. 1918 The influence of cold shock in the sterilization of canned 



foods. Jour, of Ind. & Eng. Chem. 6, 431-436. 

 Cheynet, E. W. 1919 A study of the microorganisms found in merchantable 



canned foods. Jour, of Med. Res., 40, 177-197. 

 Deichsetter, J. 1901 Ueber den Keimgehalt den Fleischkonserven. Zeitschrift 



fvir Untersuch, d. Nahr und Genussmit., 4, 1115. 

 Hunter, A. C, and Thom, C. H. 1919 An aerobic spore-forming bacillus in 



canned salmon. Jour. Ind. & Eng. Chem., 11, 655-657. 

 Lawrence, J. S., and Ford, W. W. 1916 Studies on aerobic spore-bearing 



non-pathogenic bacteria. Jour. Bact. 21, 273-320. 



