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CHAPTER V

DISINFECTION

THE object of disinfection is to prevent the extenI sion of infectious diseases by destroying the specific infectious agent (germ) which gives rise to them. This is accomplished by the use of disinfectants.

The writer, as chairman of the Committee on Disinfectants of the American Public Health Association, in 1885, defined a disinfectant as “an agent capable of destroying the infecting power of infectious material.”

In the preliminary report of this Committee the following general statements with reference to disinfection and disinfectants are also made :

“There can be no partial disinfection of such material (that is, material containing disease germs] ; either its infecting power is destroyed or it is not. In the latter case there is a failure to disinfect. Nor can there be any disinfection in the absence of infectious material.

“ Popularly, the term disinfection is used in a much broader

sense. Any chemical agent which destroys or masks bad odours, or which arrests putrefactive decomposition, is spoken of as a disinfectant. And in the absence of any infectious disease it is common to speak of disinfecting a foul cesspool, or a bad-smelling stable, or a privy vault.

“This popular use of the term had led to much misapprehen. sion, and the agents which have been found to destroy bad odours-deodorisers,—or to arrest putrefactive decompositionantiseptics,-have been confidently recommended and extensively used for the destruction of disease germs in the excreta of patients with cholera, typhoid fever, etc.

“The injurious consequences which are likely to result from such misapprehension and misuse of the word disinfectant will be appreciated when it is known that recent researches have demonstrated that many of the agents which have been found useful as deodorisers, or as antiseptics, are entirely without value for the destruction of disease germs.

“This is true, for example, as regards the sulphate of iron, or copperas, a salt which has been extensively used with the idea that it is a valuable disinfectant. As a matter of fact, sulphate of iron in saturated solution does not destroy the vitality of disease germs, or the infecting power of material containing them. This salt is, nevertheless, a very valuable antiseptic, and its low price makes it one of the most available agents for the arrest of putrefactive decomposition.

“Antiseptic agents also exercise a restraining influence upon the development of disease germs, and their use during epidemics is to be recommended when masses of organic material in the vicinity of human habitations cannot be completely destroyed, or removed, or disinfected.

“While an antiseptic agent is not necessarily a disinfectant, all disinfectants are antiseptics; for putrefactive decomposition is due to the development of 'germs of the same class as that to which disease germs belong, and the agents which destroy the latter also destroy the bacteria of putrefaction, when brought in contact with them in sufficient quantity, or restrain their development when present in smaller amounts,

“A large number of the proprietary 'disinfectants' so-called, which are in the market, are simply deodorisers or antiseptics of greater or less value, and are entirely untrustworthy for disinfecting purposes.”

The offensive gases given off from decomposing organic material are no doubt injurious to health ; and the same is true, even to a greater extent, of the more complex products known as ptomaines, which. are a product of the vital processes attending the growth of the bacteria of putrefaction and allied organisms. It is therefore desirable that these products should be destroyed; and, as a matter of fact, they are neutralised by some of the agents which we recognise as disinfectants, in accordance with the strict definition of the term. But they are also neutralised by other agents—deodorants—which cannot be relied upon for disinfecting purposes, and by disinfectants, properly so-called, in amounts inadequate for the accomplishment of disinfection. Their formation may also be prevented by the use of antiseptics. From our point of view, the destruction of sulphuretted' hydrogen, of ammonia, or even of the more poisonous ptomaines, in a privy vault, is no more disinfection than is the chemical decomposition of the same substances in a chemist's laboratory. The same is true as regards all of the bad-smelling and littleknown products of decomposition. None of these

is “infectious material,” in the sense in which we use these words; that is, they do not, so far as we know, give rise directly to any infectious disease. Indirectly they are concerned in the extension of the "filth diseases,” such as cholera, bubonic plague, and typhoid fever. This because persons exposed to the foul emanations from sewers, privy vaults, and other receptacles of filth have their vital resisting power lowered by the continued respiration of an atmosphere contaminated with these poisonous gases, and are liable to become the victims of any infectious disease to which they may be exposed.

CHAPTER VI

TESTS OF DISINFECTION

W HAT means have we of proving that the infect

V ing power of infectious material has been destroyed ?

Evidence of disinfection may be obtained : (a) from the practical experiments—experience-of those engaged in sanitary work; (6) by inoculation experiments upon susceptible animals; (c) by experiments made directly upon known disease germs.

(a) It is a matter of common experience that, when a room has been occupied by a patient with an infectious disease, such as smallpox, scarlet fever, or diphtheria, susceptible persons are liable to contract the disease weeks or even months after the patient has been removed from it, unless in the meantime it has been disinfected. If a second case does occur from exposure in such a room, it is evident that it has not been disinfected. But the non-occurrence of subsequent cases cannot always be taken as evidence

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