The prophylactic use of quinine has recently fallen somewhat into disrepute, owing to its comparative failure in many of the war areas, but there can be no doubt that under conditions of civil life it is a valuable auxiliary method, if properly employed. One of the troubles about it is that quinine is rapidly excreted from the body, and hence after a dose it remains in the blood only a comparatively short time; for example, if the dose be taken at 6 p.m. it is very doubtful if enough quinine will be left in the blood at 2 o’clock in the morning to kill any malarial spores which may be introduced into it by an infected mosquito. The ideal method of taking quinine prophylactically would be to take a dose of 5 or 6 grains with the evening meal shortly before sunset. This will protect until it is time to get under the mosquito net. If for any reason it is impossible to employ the latter, then a second dose of quinine should be taken at midnight. This is difficult to accomplish, and hence something may be gained by taking a larger dose of quinine at night on the chance that some of it may remain in the blood for a longer period than would the smaller quantity. As much as 10 grains may therefore be taken under these conditions. Some persons, however, cannot stand 10 grains of quinine daily for a long period of time. It is clear from what has been said that prophylactic quinine should never be taken in the morning, and also that it is merely an auxiliary method, and does not do away with the necessity of using the mosquito net. Sugar-coated tablets should be avoided, and care must be taken to see that the products or tablets which may be used are readily soluble. It is a good plan to crack the products before swallowing them. A good salt of quinine is the bisulphate, which is soluble and comparatively cheap. When the drug is given in powder, tablet, or pill form, it should be followed by a wine-glassful of water, and it is advisable to acidify the latter by a few drops of hydrochloric acid. There is no doubt that as a general rule quinine is best taken in solution, but in the case of persons travelling about this is not always easy to arrange, and if the above precautions be taken the solid form will generally be found effective. It is better to take prophylactic quinine in daily doses, because if an interval is allowed to elapse between doses one is apt to forget to take the drug at the proper time. Hence it is well to make it a kind of ritual to take the quinine along with the evening meal, for it is certainly an advantage to do so on a full stomach. It should be remembered that persons who take their quinine regularly do not suffer from blackwater fever, while the irregular taking of quinine certainly appears to favour the occurrence of the latter. It is better not to take prophylactic quinine at all than to take it in a haphazard and irregular manner.