106 DEPARTMENT OF THE NATAL SERVICE . 



Swelled cans, when shaken, have a characteristic " rattle." When the cans are opened, 

 gas is expelled, accompanied in advanced swellings by portions of the liquid contents. 

 The condition of the contents varies considerably. Usually the fish are macerated, 

 disintegrated, and soft, and are intermixed with the oil or sauce; they have lost their 

 entity. The odour is variable — frequently it is not unpleasant, resembling to an accen- 

 tuated dfgree the natural smell of normal sardines. In other instances a pronounced 

 putrefactive odour is evident. It may be that the putrefactive odour is present at all 

 times and is masked by the spices or other* ingredients of the sauce. That is a point 

 upon which I have no evidence. 



Examinations in the Laboratory. 



Much of the work at the commencement was done in the Biological Station, St. 

 Andrews, as already stated, and further researches were carried on principally in the 

 laboratories at Macdonald College. Using the necessary laboratory methods, a search 

 was made in the contents of both normal cans, and swelled cans for bacteria. A number 

 of varieties of bacteria have been isolated, and their characteristics determined. The 

 bacteria with which the inquiry has been chiefly concerned are those varieties or 

 types which are capable of producing the " blown " condition in the cans. If the 

 blown condition is due to the action of bacteria and not to other agencies, the 

 bacteria secured from the saanples will show that characteristic or quality in the 

 experimental work in the laboratory. The production of gas by micro-organisms' — 

 of which the bacteria are the smallest forms — is in all cases the result of the organisms 

 splitting or breaking up certain substances in order to obtain the food or nutrition 

 necessary to life. This general statement holds good if the gas is produced during the 

 digestion of food by the human subject, if it is produced in a can of condensed milk, 

 or if it is produced in a can of sardines. In order to produce gas, the bacteria must 

 have access to some form or other of carbohydrate, a very well known example of which 

 is ordinary table sugar. Hence, having secured strains of bacteria from the canned 

 sardines, the method has been to test their ability to produce gas by growing them in 

 suitable concoctions which contain the necessary amount of sugar or other carbohy- 

 drates. In this manner I found that eight strains of the bacteria secured from the 

 material examined were able to produce gas when grown in solutions containing the 

 various carbohydrates used. These eight strains were not alike in all their charac- 

 teristics, but all would split up many of the test substances. A full account of the 

 detailed studies on these bacteria is given in the more technical scientinc report on 

 the " Bacteriology of Swelled Canned Sardines," prepared by me, and published by the 

 Biological Board of Canada, Ottawa.* No bacteria obtained from the presumed 

 normal cans could produce gas in the test substances. All the gas-producing bacteria 

 were isolated from the material in the " swells " or " blown cans." 



Experimental Swelled Cans. 



The fact that gas-producing bacteria had been secured from swelled canned sar- 

 dines, and that these bacteria had produced gas in test substances used in the laboratory 

 was not proof that the bacteria involved were necessarily the causes of "swelled" or 

 " blown cans." Before it could be said that actual proof had been secured, it became 

 necessary to determine whether or not the same bacteria, when put into normal canned 

 sardines could produce the typical swelling. Accordingly a sufficient number of cans 

 of sardines which had been properly sterilized, were obtained. These cans were in- . 

 fected with a small amount of growth or culture of certain of the bacteria which had 

 been recovered from the original swells, and which had produced gas from test sub- 

 stances in the laboratory. For this purpose three of the eight strains were used. In 



•See Contributions to Canadian Biology, 1917-1918, Report XII( pp. 181-215, Supp. to 

 7th Ann. Rept. Naval Service Dept., Fisheries Branch. 



