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47
auscultation. In these days of the apotheosis of surgery I may add "exploratory
laparotomy" and Dr. Walton of Plymouth even recommends X-ray examination.
Inspection is the first and most valuable procedure. As a student I was told
again and again that "there is more missed by not looking than not knowing," and
I would commend this truism to the notice of all food inspectors.
Inspection reveals the quality, type and perhaps the age of the can; the concavity
or convexity of the ends; the methods of sealing; staining as evidence of leakage;
the presence of rust and of pinholes; evidence of venting and resoldering or the repair
of seams; denting due to ill-usage and finally the particulars of the product as described
on the label.
Palpation is of value in ascertaining whether there is a good vacuum in the tin
resulting in the ends being held firmly concave by the atmospheric pressure or whether
the ends are slack or definitely bulging.
Percussion is useful in the inspection of canned meat where the can should be
in close apposition to the contents all round so that the note elicited on tapping is
dull and non-resonant. A tympanitic or resonant note indicates the presence of gas
inside the can. In products such as fruit and vegetables the cans are not quite full,
a certain amount of head space being left. Percussion in such cans is not of much
value.
Auscultation is not carried out in the way a doctor would do it in the examination
of a patient. The food inspector's method of auscultation consists in shaking the
can close to his ear and listening to the sound, if any, thus produced. The value of
shaking depends on the nature of the product. If it is a solid product packed dry a
splashing sound would indicate liquefaction of the contents. Some canned marine
products have normally a small quantity of fluid in the can and experience is necessary
in differentiating normal from abnormal sounds on shaking. Comparison between
various cans of the same pack is often useful. In canned fruit and vegetables the
amount of head space can be estimated by shaking.
What, in order to keep to the medical terminology, I have referred to as "exploratory
laparotomy," of course, means opening up to look inside. This is a test of less value
than you might think. In the first place it can only be applied to a limited extent,
for every opened can is a wasted can so far as the merchant is concerned; secondly,
it is not possible by inspection of the contents to detect metallic contamination or
the presence of prohibited preservatives, and lastly, I contend that if after careful
external examination of a can by the methods already described the food inspector
is still suspicious as to the soundness of the contents he is justified in condemning it.
I think it is of more value to open a can here and there as a check on a favourable
external examination than to do so in the hope of confirming a suspicion of unsoundess.
As regards X-ray examination, I studied the paper which Dr. Walton read before
a Sessional Meeting of the Royal Sanitary Institute at Plymouth in February, 1935,
but it seemed to me that there was neither need nor justification for this elaboration,
believing as I do that the food inspector can, by his own observations, come to a
decision which is correct from the consumer's point of view and not unreasonably
hard on the merchant.
There has been an enormous amount of research work in connection with every
aspect of the canning of foods, in which the bacteriologist and the chemist have played
a very important part, and the canner, who originally worked empirically, now works
scientifically. Nevertheless he has not altered his criteria of soundness of his product
and I would suggest that the criteria which have been his for so long should continue
to be ours; we should not begin to mistrust them because occasionally a bacteriologist
reports the contents of a condemned can to be sterile or the chemist tells us that a
blown can is only a hydrogen swell. What the good canner aims at is the commercial
sterilisation of the food and the obtaining and maintaining of a good vacuum in the
container. I use the term "commercial sterilisation" because, though the canner
used to think he got absolute sterilisations, we now know that in many cases he does
not, and indeed that, with certain foods, he could not, without using a degree of heat