The glutinous membrane of which frequent mention has been made above, is of a very viscid nature, and when combined with any animal substance in a state of transition or fermentation, it is poisonous. It is, I believe, generally viewed as the matrix for the development of the ova of these shell fish, and considered as a product or secretion of the parent. Into this question I enter not, leaving it, if it be one, to others. On exposing for a few days some of the larger testaceous mollusca alive to the atmosphere of the room at a temperature varying from 65° to 70° Fahr., strong proofs were obtained that ammonia was produced in the interior of the shell confined therein by the membrane called operculum, sealing, as it were, the aperture into the shell hermetically. On puncturing this membrane the presence of ammoniacal gas could be distinctly traced by the odour. I submit to the consideration of professed physiologists the following questions:--1st. What are the effects likely to result to man from the inhalation of these microscopic and gaseous products in a state of decomposition, they being certainly present in the vapours arising from the waters of canals, ditches, &c., in many countries, especially during the nights of spring, summer, and autumn? 2nd. What are the evil effects likely to arise to man from the use of such waters as drink, or when employed for culinary purposes? Lastly: As the gelatinous membranes alluded to are the nidus of various forms of organic life, and contain those forms, developed and undeveloped, occasionally in a state of decomposition, to which of the two forms of life, animal or vegetable, or to both, is to be ascribed the deleterious effects on man, and ascribed by physicians to an unknown poison called Malaria, designated by them as “a poison, an influence, a miasm, a thing unknown”? Ferments and putrescence are not “things unknown:” let us adhere to facts. § 2. Thus the principle of wasting away by the action of the atmosphere, of the rotting of vegetable and animal substances, first developed by the illustrious Liebig, opened up to me the path to that theory which seems to reconcile the conflicting observations of pathologists,--that vegetable and animal matters do ferment or rot, and that in this state of rottenness they are carried through the air, was with me no longer a matter of doubt; next came the question, as to the effects of such matters on man when inhaled by respiration and conveyed directly into the living, circulating blood, that most complex of all fluids, that mysterious compound out of which nature constructs the animal world.