EXAMINATION OF CANNED FOODS 511 
Baker states that the analyses of probably 100 samples of gas from 
sound cans has never shown any oxygen. He attributes this to the 
oxidation of tin and iron salts, and combination with nascent hydrogen. 
Springers. Bigelow (1914) defines a springer as a ‘‘ can whose ends 
are more or less bulged, owing to pressure from hydrogen generated as a 
result of the chemical action of the contents on the metal of the con- 
tainer or because the can was overfilled or insufficiently exhausted.” 
Cans with bulged ends may be caused by expansion due to a rise in 
temperature. These will soon return to normal shape when the tem- 
perature is lowered. Baker (1912) states that the gases in the head 
spaces of springers are never more than three; carbon dioxide, nitrogen 
and hydrogen. Often hydrogen is absent and oxygen is rarely found. 
Flat Sour. This is a general term and may be used to cover many 
abnormalities of canned goods. Flat sours contain no gas and since 
there is nothing to indicate any abnormal condition when looking at a 
can, their discovery is delayed until the can is opened. 
EXAMINATION OF CANNED Foops 
The examination of canned foods is accompanied with danger unless 
the examiner has had experience in interpreting his data, both chem- 
ical and bacteriological. Bigelow (1917) has pointed out this side of 
the question very strikingly. The methods which are used are quite 
similar to those used in other branches of bacteriology. The objects 
of the examination may be varied. Quite often it is to determine the 
sterility of certain foods in order to check up the process of manufacture; 
or the yuality of raw materials may be the object. The examination 
of canned foods presents the same difficulty that Pennington has men- 
tioned with regard to the examination of eggs: the examination of one 
can or one egg may not yield information with regard to other cans or 
eggs. Each must be regarded as a sealed package and when once 
opened may be brought back to the original condition with a little 
difficulty. 
The bacteriological examination of canned foods has been fully 
discussed by Bitting and Bitting (1917). Some of the discussion below 
has been taken from that paper. 
The first step in the examination is to observe the appearance of the 
can. Rusty cans suggest the possibility of perforations. The cans 
should be without dents and with slightly concave or flat ends. In 
certain cases bulged ends may be due to springers, which will go down 
