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1. The sympathetic nervous system and the adjuvant adrenalin-secreting system are found in their earliest form in the annelid kingdom, and consist of cells situated in the central nervous system which are the common ancestors of both, and which are both secretory and nervous in function. 2. These cells are developed in the annelid kingdom parallel with the development of a contractile vascular system, which possesses muscles comparable in physiological actions with the muscle of the vertebrate heart. 3. This vascular muscle is regulated by the processes of the common ancestral cells as well as by their secretory activity. 4. In the primitive form contractile rhythm is an intrinsic property of cardiac muscle; its nerve supply regulates the rhythm, it does not initiate it. The beat is therefore myogenic, not neurogenic. 5. The contractile vascular system of annelids is mainly branchial in function. The vertebrate heart has been derived from it by the growing around of the lateral body folds to form a new ventral surface.

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TIIE relationship between virulence and pulmonary lesion has already been describeci in this Journal (Gaslrell 1925) in a pneumococcus of type I. Further work with other strains of type I pneumococci, isolated from human sources, has confirmed the view that organisms of this type produce lesions both in the experimental rabbit and the human subject in agreement with the relationship there set forth. The niinimal lethal dose to mice being used as a measure of titre (Gaskell 1924) organisms of titre lower than 4 have practically no pathogenic effect; from 4 to 5 a bronchopneumonia is produced; a t about titre 5 a more extensive lobular lesion occurs; from 5 to 6 a lobar lesion takes place with or without extensive invasion of the pleura: and pericardium, which often renders the lobar lesion incomplete; from 6 to 7 a rapid direct invasion of the blood produces a true septiczmia with characteristic changes in the lung quite different in type.I n man, perhaps owing to the larger size of the lung, the invasion of the serous cavities, the pleurre and pericardium, is much more uncommon than in the rabbit and a lobar lesion is usually produced at titre 5 to 6 ; the septicEmic lesion is much more uncommon, except as a sequel to a true lobar lesion, but is found occasionally in children (Armstrong and Gaskell 1921). Whittle (1928) has estimated the titre of the pneumococci isolated from a number of cases of type I invasion in man and finds that the titre relationship closely corresponds to the above scale.The experiments to be described in this paper were undertaken in the expectation that pneumococcal type was of little importance from the pathogenic point of view, and that similar lesions could be produced experimentally in rabbits with pneumococci of type I1 and I11 and virulent organisms of group I V as easily as with type I. It was found however that the strains of such types which had been selected for experiment did not exactly conform to the behaviour of type I organisms ; both the type I1 and I11 pneumococci were not only more JOURN. OF PATH.-VOL. XXXI. S 2 R