is the distinguishing mark that they act independently of the quantity introduced into the body. This again cuts off all inorganic and organic stimuli and natural secretions not already disqualified by their liquid or gaseous nature, and leaves only the ferments and the contagia.

§3. Now, there are two distinct kinds of ferments, both of which may be said to display the last character, viz., the chemical ferments which catalytically excite an indefinite amount of change in other bodies without being themselves decomposed in the process; and the organised ferments which produce changes in virtue of their vital activity and growth as living organisms. The application of the same word, fermentation, to these different processes is one cause of the confusion in which the so-called germ-theory is involved, and which can only be avoided by keeping in mind the cardinal distinction between them, which is, that the chemical ferments, besides being soluble, and acting almost instantaneously at a very wide range of temperature, are not reproduced during their activity, whereas the organised ferments are reproduced therein.

§ 4. Now, although all living matter is particulate, and all contagia may be assumed to be particulate, and nothing reproduces itself except living matter, yet it does not follow that contagia must necessarily be living. For it may be that certain non-living morbid secretions may simply be capable of exciting in other persons a similar morbid secretion as specific stimuli not containing in their own nature, as living matter, the explanation of their reproduction. This would be simply to state the facts of contagion in the sense of its being a non-parasitic pathological phenomenon without any attempt at explanation. But, especially considering the minimal dose, there are good grounds now for looking for the explanation in the hypothesis of the living nature of the contagion itself. Granting, therefore, the possibility of this,

remittent marsh fevers. Here the poison develops itself externally to the body, and is not reproduced therein so as to affect other men from thence, nor is it excreted thence to propagate itself in any other way. 3rd. The miasmatic-contagious comprehend cholera, typhoid, dysentery, and probably some others; here the disease is not readily, if at all, transmissible from person to person; nevertheless, these diseases never originate spontaneously or from purely malarious influences, but always after some person affected with them has been in the neighbourhood; so it is supposed the secretions from infected persons undergo development in favourable media out of the body. In other words, the reproduction of the miasm is partially performed out of the body.

§ 2. What is the intimate nature of this miasm or infectious matter? In the first place, as regards its physical state, it has been determined with respect to the vaccine and some other animal poisons, and is almost certain with the rest, that the specific power does not reside in anything which is gaseous, or liquid, or capable of solution, or diffusible from the medium in which it is contained. * Thus when we hear of sewage or paludal liquids or gases spoken of as the exciting causes of infectious diseases, it is to be understood that the true specific matter is a solid merely suspended in the liquid or gas. This at once cuts off a large number of both inorganic and organic substances from the category of possible causes of the specific disease. [See diagram]. Next

*Dr. Lionel Beale first attributed the infective properties of vaccine and other contagious diseases exclusively to solid matter, and this was experimentally demonstrated afterwards, first by Chauveau and then by Dr. B. Sanderson, by the method of diffusion. Filtration was ineffectual for separating the extremely minute particles in which the contagion resides, from the matrix fluid. Chauveau found the same principle to apply to variola, pleuro-pneumonia, glanders, and sheep-pox. The experiments with the vaccine matter have been recently repeated with greater care and detail by Drs. Braidwood and Vacher, of Birkenhead, who have proved that the liquid diffused out from vaccine matter is totally devoid of infective power.

is the distinguishing mark that they act independently of the quantity introduced into the body. This again cuts off all inorganic and organic stimuli and natural secretions not already disqualified by their liquid or gaseous nature, and leaves only the ferments and the contagia.

§ 3. Now, there are two distinct kinds of ferments, both of which may be said to display the last character, viz., the chemical ferments which catalytically excite an indefinite amount of change in other bodies without being themselves decomposed in the process; and the organised ferments which produce changes in virtue of their vital activity and growth as living organisms. The application of the same word, fermentation, to these different processes is one cause of the confusion in which the so-called germ-theory is involved, and which can only be avoided by keeping in mind the cardinal distinction between them, which is, that the chemical ferments, besides being soluble, and acting almost instantaneously at a very wide range of temperature, are not reproduced during their activity, whereas the organised ferments are reproduced therein.

§ 4. Now, although all living matter is particulate, and all contagia may be assumed to be particulate, and nothing reproduces itself except living matter, yet it does not follow that contagia must necessarily be living. For it may be that certain non-living morbid secretions may simply be capable of exciting in other persons a similar morbid secretion as specific stimuli not containing in their own nature, as living matter, the explanation of their reproduction. This would be simply to state the facts of contagion in the sense of its being a non-parasitic pathological phenomenon without any attempt at explanation. But, especially considering the minimal dose, there are good grounds now for looking for the explanation in the hypothesis of the living nature of the contagion itself. Granting, therefore, the possibility of this,

we are now by the above process of exclusion restricted to three known substances:-1st, parasites, already known as such; 2nd, the organised ferments; 3rd, portions of altered protoplasm, or living matter capable of transplantation and subsequent growth in the bodies of other persons; here called partial bions or graft-germs. Now, as the organised ferments are independent animal and vegetable beings, with their proper life history and mode of reproduction, they would necessarily come into the category of parasites if capable of running their course within the higher animals. The exciting causes of infectious disease is thus narrowed into two categories, viz., Parasitic-germs and Graft-germs. [See diagram]. An immense step is thus made in unveiling

* It will clear up the subject amazingly if we set aside the questions of fermentation and spontaneous generation from all connection with infectious diseases. The superficial resemblance between the specific fevers and the process of fermentation is false and misleading, and it is unfortunate that the name of Zymotic should be sanctioned by authority as applied to those diseases. The true chemical ferments are recognised as agents which break up, with or without combination with oxygen, dead chemical matters by a purely chemical or non-vital process. There is no proof or probability that any chemical agent acts or could act thus on the living tissues or blood in the production of disease. And the sole analogy between the action of a contagious miasm and a chemical ferment is the circumstance of their both acting in minimal dose. From very different causes however; the organised ferment reproduces itself, and is thus multiplied indefinitely, while the chemical ferment simply acts over and over again without addition of new particles, and hence the analogy with a contagious miasm quite fails. There is a fallacy in the common mode of comparing the action of a chemical ferment to disease. For example, it is said, a single drop of septicemic blood introduced into the blood of a healthy animal acts like a ferment which, without being itself consumed, alters the whole blood and kills the animal. Again, a drop of the blood of this last animal (containing thus a mere fraction of the original drop) may alter the whole blood of a second animal and kill it. And so on indefinitely, always because an indefinite quantity of blood can be split up catalytically by the ferment, in however small a dose, seeing that it is not consumed in the process. This mode of statement involves several assumptions, and is contrary to the facts. For the natural ferments require a certain degree of concentration, and will not convert an unlimited quantity, and are slowly consumed or absorbed in the process, thus requiring renewal by secretion. If the second

the mystery which has hitherto enveloped the mode of propagation of infectious diseases. For such germs being exceedingly minute, in fact, ultra-microscopic, it is easy to see how they can be spread abroad unsuspected in every variety of vehicle, and their power of survival, as well as their liability to destruction, corresponds accurately to what is known in these respects of the fomites of contagia. Their conveyance by solids and liquids presents no difficulties, but until lately it was not possible to trace them in the air, and, accordingly, numerous telluric and imponderable influences were imagined as the cause of the origin and spread of infectious diseases. But it has been demonstrated by the admirable experiments of Tyndall that all ordinary air contains ultra-microscopic and succeeding generations of the poisoning were really caused by fractions of the original drop, the disease would be gradually slower and less virulent in its progress, whereas the exact contrary is the case. Besides, the known chemical ferments can hardly be called poisons, and even if injected into the blood would not be injurious except in far greater quantity than the contagia require; and therefore the law of minimal doses does not apply, while any injurious effect they may thus have is no doubt solely that of noxious foreign matters, of which any considerable quantity of any kind is injurious thus introduced. There is no proof whatever that they act as ferments when thus hurtful, and to assume that the contagia are chemical ferments of an unknown nature which may so act on the non-living part of the blood, is simply a gratuitous hypothesis. Thus, while failing to account for the cardinal phenomenon of multiplication of the contagion, the chemical ferment theory fails equally to account for the immediate operation of animal poisons.

On the other hand, the so-called organised ferments perfectly meet the cardinal point of reproduction; but even supposing they are proved to be the cause of contagious diseases, how far can this operation be compared to their effects on dead organic matter known as fermentation and putrefaction? In these processes it is obvious the fermentive and putrefactive organisms may act in two ways:-1st. They may secrete a chemical ferment which may do all the work chemically; or, 2nd, they may, as a vital process, consume the fermentable substance as other living creatures do pabulum, and the products, viz., alcohol, carbonic acid, ammonia, succinic acid, &c., may simply correspond to the urea carbonic acid, water, &c., given off by the higher animals. Now, it is proved that yeast does secrete such a chemical ferment, and it is highly probable that the bacteria do so also, and it may be accepted that the living ferments operate in both these