Some Bacterial Organisms occurring in the Clam (Mya 
Arenaria) which may produce ‘“Blackening” in Tins. 
By JENNIE L. Symons, M.Sc., 
(McGill University, Montreal). 
The problem of blackening is a serious one in the canning industry. 
Blackening is a common form of deterioration, in advanced stages of which the 
contents of the tin becomes inky black and disintegrated. There is an intense 
disagreeable odour in which a metallic quality is combined with the odour of 
putrefaction. Often there is a large amount of gas, causing the cans to be 
swelled as well as blackened. 
The cause of blackening is usually accepted as bacterial action. It has long 
been studied from this point of view. In 1897, a paper on “ Discolouration in 
Canned Lobsters’? was published by Macphail and Bruére.! The authors had 
isolated from spoiled cans four micro-organisms which, upon inoculation into 
sterile cans, produced the blackened condition. Prescott and Underwood’, in 
the same year, isolated from swelled tins of clams and lobsters nine species of 
bacteria, which led to similar conditions if introduced into normal cans. These 
organisms were found to be very resistant to heat. The authors of both papers 
pointed out the necessity of accurately determined minimal periods of processing. 
This determination involves a study of the bacteria concerned. It is also import- 
ant to know the source of the micro-organisms which appear in the cans in order 
to ascertain the chances of preventing infection. 
The investigation described in this paper was undertaken at the suggestion 
of Dr. A. G. Huntsman, Curator of the Atlantic Biological Station at St. Andrews, 
N.B. Its aim has been a bacteriological examination of freshly dug clams 
(Mya arenaria), such as are taken to the factories for canning, with a view to 
the isolation and description of any blackening organisms normally present in 
such clams. 
PROCEDURE. 
Isolations. 
The clams from which isolations were made were of medium size. They 
were dug at low tide on the beach near the Biological Station and brought in at 
once. The exteriors of the shells were thoroughly washed in a stream of running 
tap water and dried in the air. The edges were then seared in a flame and the 
muscles holding the shell quickly severed with a knife.* One half of the shell 
was then removed, the clam lying in:the other half. The mantle was slit and 
turned back and four small pieces cut* from the body of the clam were at once 
transferred with forceps* to separate tubes of broth. Cuttings were thus made 
* All knives, scissors and forceps used for these purposes were kept standing in a jar of 
alcohol and sterilized by flaming immediately before use. 
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