According to Koch, his remedy, consisting of a brownish liquid, is easily perishable as soon as it is diluted with water; he recommends the preparation of the dilution of the remedy with a 5 per cent. phenol solution. Phenol is equivalent to carbolic acid. The dilution of the remedy for use must be considerable, as only small quantities of the same are used.
Koch tells us that his remedy does not act through the stomach, that is taken in through the mouth. On one hand it may be that this is due to the extremely small quantities necessary for an effect, on the other hand and principally all the substances probably act only when they are directly applied and brought in contact with the circulation of the blood.
For a long time small syringes with fine needle points were used to inject strong acting drugs under the skin. This is done in a measure to have a guarantee of a sure effect which is not had by giving through the mouth. For instance, it is known that emetics given through the mouth often remain without results; if however the emetic apomorphine is injected anywhere under the skin, vomiting surely follows within a very short time. It is well known that morphine is injected under the skin in preference to taking it through the mouth as its action as a pain killer is much prompter.
Koch's liquid can also be injected under the skin with the aid of a so-called Pravaz syringe. Koch uses a somewhat differently formed syringe. The result remains the same, no matter what kind of syringe is used.
At the same time it makes but little difference, on what part of the body the injection is made, as the fluid injected under the skin is distributed at once over the entire system. Koch chose the skin of the back between the shoulderblades and the loins because here the injection could be made without causing pain or inflammation.
The production of the liquid must be attended with great difficulties as Koch plainly remarks that his stock at present is very limited and he can only furnish larger quantities at the end of several weeks. The price of a small bottle to be 25–30 Marks about 6–8 Dollars.
The human being is much more sensitive to Koch's remedy than the guinea pig, which is commonly used for experiments of this kind. It seems that no experiments have as yet been made with other animals.
Koch has tried the remedy on himself and has passed through all the symptoms of a poisoning. He certainly injected into his arm a considerable quantity of the liquid; twenty-five times as much as he injected in his patients.
But here also there is a difference. In sick people much smaller quantities act than in the healthy. One cubic centimeter of the liquid has hardly any effect on a healthy person, but quite a marked one on those afflicted with tuberculosis.
In the case of the latter one cubic centimeter produces about the same symptoms as twenty-five times the quantity would in a healthy person. The same must also be considered as symptoms of poisoning; but they are only of short duration and are accompanied with magnificent success.