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 76 he felt he did not understand; as, for ex- ample, in what is known (out of England, at least) as the « Problem of Harvey ' (see De Partu, pp. 132, 549, ed. 1766; p. 530, ed. Willis) — a problem which, I think, could not have been answered till the • works and days ' of Bernard p ; and in the cases of P I refer to Claude Bernard's experiments on the in- fluence of vitiated air (Des Effets des Substances Toxiques et medicamenteuses, 1857, p. 125), which show so plainly that organisms can attain a power of tolerance as against morbific agencies if time is allowed them to become gradually adjusted to such environment. The principle demonstrated in these experiments has been brought into greater prominence by Sir James Paget in his striking account (Lancet, June 3, 187 1 ; p. 734), so interesting to all of us for other than purely scientific reasons, of his serious illness in 187 1. As regards the 'Problem of Harvey,' the foetus in ulero has been habituated to lowly arterialised blood ; the blood of the umbilical vein is not scarlet in colour, and hence, I submit, may be explained the tolerance by a child which has come into the world but has not yet breathed in it, of conditions which entail death by suffocation in a child which, having breathed air, is exposed to them. This physiological principle has, amoilg many other practical bearings, the practical value of furnishing an answer to the Philistine argument so often brought forward by Antisanitarians in favour of the re- tention of abuses, in the words ' see to what a good old age people live in the middle of it all !' The answer is,