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1. In investigating a spontaneous epidemic disease of rabbits, a micro-organism was isolated in pure cultures which reproduced the characteristic lesions of the natural disease.
2. The bacteriological characters of this bacillus are described and the impossibility of identifying it with previously recorded organisms justifies its being considered a new species. The name Bacterium monocytogenes is proposed.
3. Animal passage raised "virulence" when the doses were well chosen, and increased virulence accentuated the production of necrotic lesions. Overwhelming doses of culture resulted in lowering of "virulence" by animal passage.
4. Bacterium monocytogenes, in doses less than the M.L.D., produced in the circulating blood of rabbits an extreme monocytosis. The responses of the other white cells. were either transient or inconstant.
5. Repeated doses of the organism became progressively less effective as stimuli to large mononuclear production.
6. The cell content of the thoracic duct did not reflect the high degree of monocytosis in the circulating blood.
7. On intrapleural injection of peptone broth and B. coli, the cells of the resultant exudate were primarily polymorphonuclears, even though the circulating blood showed a high monocytosis. With intrapleural injection of B. monocytogenes, when the blood stream was rich in large mononuclears, a pleural exudate containing 30 per cent of these cells was obtained.
8. Phagocytosis experiments in vitro showed that the large mononuclears, while they phagocyted B. coli indifferently, took up B. monocytogenes with an avidity in all respects equal to that of the polymorphonuclear neutrophiles.
The objects of this work were to reinvestigate and extend the results announced in a brief note published in 1925 (Murray and Huxley, 1925a). In this paper it was concluded that isolated fragments of the limb buds of the fourday chick are able to self-differentiate when Iiving as grafts on the chorio-allantoic membrane of older chicks; that the bud of the four-day chick is a mosaic; it was hinted that each of the morphological regions of the limb (femur, tibia-fibula, etc.) is represented by a Single piece of the mosaic; that no regeneration or regulation occurs in fragments of the bud, except that it was concluded that if a grafted fragment contains only part of a piece of the mosaic, that part could so regulate its future development as to form the complete morphological region of which it was originally a part, so that a fragment of the bud which contains part only of the region Which would normally form femur will, when growing as a graft, form a complete femur. It will be seen that the results of the present work uphold and confirm the tentative conclusions previously advanced, except in regard to the last point (regulation). A considerable amonnt of further information has also been obtained bearing on tile factors concerned in the development of the form of bones and joints.