The Milroy lectures on epidemic diseases in England : the evidence of variability and of persistency of type delivered before the Royal College of Physicians of London, March 1st, 6th, and 8th, 1906 / by W.H. Hamer.

  • Hamer, William Heaton, 1862-1936.
Date:
1906
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Licence: Public Domain Mark

Credit: The Milroy lectures on epidemic diseases in England : the evidence of variability and of persistency of type delivered before the Royal College of Physicians of London, March 1st, 6th, and 8th, 1906 / by W.H. Hamer. Source: Wellcome Collection.

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    portant knowledge, is never adequate to establish, on the foundation of actually-observed phenomena, a doctrine of diseases worthy of the name.” In the first instance, it is necessary to lay down a scale indicating the rate at which forms of life may be presumed to vary. On the one hand there is evidence of extraordinary persistency of type. “ What is more certain,” says Weis- mann, “ than that the animals and plants around us remain the same as long as we can observe them, not through the lifetime of an individual only, but through centuries, and in the case of many species, for several thousand years. Certain genera of echinoderms, such as starfish (Astro- pecten), lived in the Silurian times, and they are represented nowadays in our seas by a number of species ; and in the same way the cephalopod genus Nautilus has maintained itself among the living all through the enormous period from the Silurian sea to our own day. Similarly, the genus Lingula of the nearly extinct class of brachiopods has been preserved from the grey dawn of primitive times, with its records in the oldest deposits, and is represented in the living world of to-day by the so-called ‘ barnacle goose’ mussel, Lingula anatina.” Huxley was fond of insisting upon the existence of what he called “ persistent ” types, and as long ago as 1862 he argued in a strain which shows that some of the doctrines enunciated by Sir George Darwin and Weismann were already accepted by him. He says that study of the positive facts of palaeontology impresses us not with the greatness of the changes which are exhibited to view, but with the “ smallness of the total change.” Thus, “ there are 200 known orders of plants; of these not one is certainly known to exist exclusively in the fossil state. The whole lapse of geological time has as yet yielded not a single new ordinal type of vegetable structure.” The change in the animal world, though greater, is still singularly small. “ No fossil animal is so distinct from those now living as to require to be arranged even in a separate class from those which contain existing forms. It is only when we come to the orders, which may be roughly estimated at about 130, that we meet with fossil animals so distinct from those now living as to require orders for themselves, and these do not amount, on the most liberal estimate, to more than about ten per cent, of the whole.” Aofain, he refers to a lecture “ On the Per- sistent Types of Animal Life,” delivered in 1859, in which