The foregoing observations naturally lead one to the question of frequency and distribution. Davaine holds that the comparative infrequency of this parasite in Paris is due to the free use of the filter. In London, though not uncommon, the worm rarely occurs in great numbers in one bearer. Those cases in our hospitals, where considerable numbers have been present, have usually come up from suburban or country places. Heller states that these worms were found in 9·1 per cent. of post mortems conducted at Dresden, in 12 per cent. at Erlangen, and in 17 per cent. at Kiel. He quotes Huss as stating that no one is free from this worm in Finland. The prevalence of large round worms in warm countries generally is well known. Throughout India and the East they are extremely abundant, and the same may be said of the West Indies, Brazil, and the adjacent territories. Professor Dyce and others have remarked on the extreme prevalence of lumbrici in the Mauritius, but they are comparatively rare along the sea border. In all situations where there is an abundant fresh-water supply these parasites are particularly common, as in the lowlands of Holland and the lake districts of Sweden. The abundance of water is certainly not alone sufficient to explain the frequency of the parasite, seeing that the most important factor is that which rests upon the uncivilised habits of the rural population. What, therefore, it may be asked, can be the cause of immunity enjoyed by Icelanders in this respect? The answer is not apparent; nevertheless Krabbe and Finsen have testified to the fact that Iceland is the only country that is entirely free from _Ascaris lumbricoides_. As remarked in my previous work the number of worms present in any human bearer is usually small, varying commonly from one to six or eight. Cases in which scores or hundreds have existed are comparatively rare. Küchenmeister mentions the case of one child who passed 103 examples, and of another child that harbored from 300 to 400 worms. Dr Gilli, of Turin, gives a case where 510 were passed by a child, and Cruveilhier estimated that over 1000 existed in an idiot girl, whose intestines he found crammed with them. A remarkable case has also been communicated to me by Dr Mackeith, of Sandhurst, Kent, who, by means of santonine, expelled from a little girl, five and a half years of age, 300 lumbrici; and I am likewise indebted to Dr Cooper Rose for notes of a case in which about thirty lumbrici were expelled, chiefly in consequence of the employment of this drug. The most interesting fact, however, in this case was that the child was only fifteen months old. In this case the symptoms were severe.