Prevention is of vital importance. The flea is the medium by which the disease is conveyed to man from infected rats. Hence the importance of exterminating these rodents by trapping, by poisoning, by cats, by asphyxiation with sulphur and other methods. Of all the means of em ploying poison none is so efficacious and less dangerous to man than the employment of the Danysz virus. It must be remembered that though all the species of rat-fleas do not bite man, the fleas which infest the human subject and many domestic animals will also bite the rat and become infected, thus conveying the pestilence to the human being.
The parasites leave the body of the infected rat and may travel in clothing or merchandise; hence the importance of the disinfection of all baggage coming from infected ports.
In pneumonic plague the infection is direct from one human being to another, and therefore the rigid isolation of all sufferers is of more vital importance than in the bubonic type.
To isolate the shore rats from those arriving in infected ships the system of placing effective shields or guards on all cables should be rigidly carried out, and when possible the vessels should be prevented from coming in close to the landing-stage. It is needless to state that every precaution which sanitary science can suggest for the improvement of hygiene, the establishment of cleanliness and the protection of all food supplies from being soiled by the excreta of infected vermin must be established in sea ports liable to be exposed to the dangers of invasion. The bodies of all captured or poisoned rats should be cremated without delay.
Vaccine therapy as a preventive is of unquestionable utility. Haffkine's Plague Prophylactic consists of a six weeks' culture of the bacillus, killed by heat and preserved by the addition of per cent. phenol. r c.c. of the Lister Institute preparation should be injected subcutaneously and may be repeated in about 12 days. Immunity is conferred after 7 days and lasts for many months; this is not, however, complete or absolute, but the proportion of " protected " individuals who afterwards contract plague is a small one, and the mortality amongst them is comparatively trifling.
The vaccine is, however, of no value as a curative agent once the disease has appeared in an unvaccinated victim, notwithstanding that the saving of life is enormous in times of the pestilence by resorting to early inocu lation.
The treatment of the established disease remains at present mainly symptomatic, Yersin's curative serum having to a large extent failed in fulfilling the high expectations aroused upon its introduction. This serum is prepared at the Lister Institute from horses injected intraven ously by virulent cultures of the plague bacillus. The dose is 5o c.c. injected into the veins of the patient as soon as the first symptom of plague shows itself, ioo c.c. being at the same time injected subcutaneously and repeated in 12 to 24 hours, 25o c.c. being injected within the first 24 hours. Dixon. states that this dosage is much too small, and he injects intraven ously up to 130 c.c. until a rigor is produced. Though many observers maintain an attitude of scepticism about the curative value of Yersin's serum, others affirm that when administered in full doses upon the first day of the disease the entire clinical aspect improves. As regards the evidence of its curative virtues, there is still a wide divergence of opinion, but perhaps the most significant fact about its value lies in its acknow ledged failure as a prophylactic, and its uselessness when resorted to after the first or second day of the established disease. In mild epidemics where the serum has been administered as a routine, the mortality it is claimed has been markedly reduced, but these are obviously the circum stances under which a low mortality is to be expected. The intravenous injection of Tincture of Iodine has been recommended lately, hut further corroboration of its virtues are awaited. The symptomatic treatment of plague must therefore be resorted to in every case, whether or not Yersin's or the Yersin-Roux antiplague serum has been injected.