Origin of Disease - Germs - Essentials of a good Disinfectant - Carbolic Acid - Cyllin-Jeyes' Fluid - Sanitas-Formalin - Formaldehyd - Sulphur - Per chloride of Mercury - Condy's Fluid - Formamint - Iodine - Zinc - Nitrous Acid - Fumes - Euchlorine - Public Disinfection - Washington-Lyon's Disinfector.

When we recall the dreadful diseases, such as cholera, plague, black death, and typhus fever, which raged in Europe throughout the Middle Ages, we cannot be too thankful that during recent years preventive medicine and the science of bacteriology have been successfully studied. The laws of hygiene too have been obeyed, and now in England zymotic diseases due to filth, starvation, and overcrowding, are practically stamped out. Scarlet fever, measles, and other ordinary epidemics are now treated so promptly and efficiently that the number of fatalities is enormously reduced.

The origin of epidemics is due to micro-organisms or germs, not by their mere presence in the body, but by their production through chemical changes (as they live and multiply) of certain poisonous substances which constitute the true infectants.

The microbes are divided into three classes-

1. Rod-shaped organisms known as bacilli.

2. Curved bodies called vibrios, or where several are linked together, spirilla, and

3. Minute spherical masses called cocci. These are so microscopic that 125,000 would have to be laid in a row touching each other to form a line one inch long.

The universe abounds in germs of all sorts, and we are constantly exposed to their action, breathing into our bodies millions of them every day, but ordinarily if our blood is in good condition our bodies present a sufficient resistance to prevent them from doing any harm, while the good done by many of them is enormous, for it is by their direct agency that all dead organic animal and vegetable matter is finally resolved into simpler chemical products, which become available again in turn to serve as foods or nutrients for vegetation.

We, however, are dealing with the poison-producing germs which cause their respective diseases, as it is for these only that germicides are required.

DISINFECTANTS have a distinct and definite mission-

1. To quickly and entirely destroy the germ which is causing the poison.

2. To also kill the spores or immature germs. ANTISEPTICS have not this definitely destructive power; their work is to prevent the multiplication of such disease-producing germs.

DEODORANTS merely mask or absorb certain undesirable odours and vapours which accompany the putrefaction of dead organic matter and have no necessary action on bacteria.

Fresh air, sunshine, light, and cleanliness are all essential in the prevention of sickness, and they all help towards the enfeebling and suppression of the germ, but the microbe's ubiquity and great power of endurance render some chemical agent necessary for their destruction.

The following are the requisites of a good disinfectant.

1. It must be a real and active germicide, capable, even in dilute solutions, of destroying all kinds of bacteria.

2. It must retain its efficiency in the presence of organic matter.

3. It must be non-poisonous in every practical and reasonable way.

4. It must be free from any caustic action on the skin even in a pure state, not only for the patient's sake, but to maintain the delicacy of touch necessary for the nurse.

5. It must be readily soluble in water, so as to be capable of diffusion in a diluted condition over large areas.

6. It must be cheap if intended to be generally and extensively used.

7. It is desirable that it should not stain linen or destroy colour.

8. It is of the greatest importance that it should be wholly uninfluenced in its action by the presence of either soap or serum.

In hospitals, where there is practically an inexhaustible supply of hot water, this last consideration is not so important, but in the case of a poor home where, perhaps, only a kettleful of water can be procured, which must serve for the washing and cleansing of the wound, also for rinsing away the soap used for this purpose, there is grave objection to the use of any disinfectant of the nature of perchloride of mercury which is absolutely useless in the presence of blood-serum or of soap.

The choice of disinfectants is of great importance, and medical opinion concerning them has greatly changed during recent years. At one time it was believed that the coal-tar disinfectants, for example, depended for their efficacy upon the carbolic or cresylic acid which they contained, and that a direct ratio existed between the efficiency and the quantity present. Now, it must be remembered that the disinfectant value of a solution does not necessarily vary with its concentration, and that for many solutions there is a point beyond which increased concentration not only does not add to, but actually reduces their disinfecting effect.

Carbolic, cresylic, and other coal-tar acids, which have been in use for many years are to a very large extent being superseded by more powerful germicides which are less poisonous both to mankind and animals.

In 1903 the Rideal-Walker test was instituted, and the comparative germicidal values of various disinfectants was tried, with the result that the aforesaid acids were found wanting in some of the necessary qualifications.

The precise mode of action of disinfectants must necessarily be various in character. For instance, in addition to its valuable power of oxidation, peroxide of hydrogen acts as a direct poison to germs of the putrefactive type, but it asphyxiates some microbes by its active oxygen, just as carbolic acid acts as a direct poison to man. Some preparations (such as pyrogallic acid) act in exactly opposite manner - namely, by absorbing the oxygen necessary for the life of the microbe. Other chemical agents (such as tannin and alum) render the medium in which the germs exist unfit for their further sustenance and thus starve them out of existence.