Blaxall6 has introduced the admixture of clove oil with glycerine and water mixture, in the proportion of l per cent. He finds that the lymph, containing clove oil, is much more rapidly purified, so that a much shorter storage is necessary. No reduction in the potency of the lymph has been noticed, in his hands, by this method.
A trial of the addition of 1 per cent clove oil was made at this Institute, but it was found that the action of the clove oil was very uncertain, in the case of the lymph produced here. The purification where clove oil was added, was more rapid than in the case of glycerine alone, but a certain number of lymph numbers proved very resistent and considerable numbers of organisms were still present after many weeks' storage. It seems a risky procedure to store a living vaccine containing an active disinfectant such as an essential oil. One would expect the active virus to be injured ultimately, and our experience of the method tends to confirm this to some extent, though, in view of Blaxall's work, its action must be very slow. Its use was, however, discontinued in favour of chloroformed lymph. Experiments were also made with glycerinated lymph, which was kept for a week or longer at about 50° F., till the extraneous germs were reduced sufficiently and then placed in cold store below freezing point. The results obtained by this method were not so good as in the case of chloroformed lymph.
In fact, the results obtained with glycerinated lymph, purified by chloroform according to the methods used at this Institute, have proved so excellent that all other methods have been given up for routine work. Rapidity of purification, by this method, is a great advantage, as experience has amply demonstrated that a certain proportion of vaccine lymphs, unless stored at very low temperatures, tends to decrease in potency the longer it is stored. So that, where lymph has been stored for any period over three months, it is found uncertain as regards its potency, and it cannot be issued, with safety, without previous trial on children to ascertain its activity.
Our experience at Belgaum is that, where a series of lymph numbers, collected from calves showing vesiculation of the same quality and treated in an identical way throughout the different processes, are stored under the same conditions, a small proportion of these lymph numbers will show marked deterioration, after four months' storage, while the remaining larger proportion will have retained its potency slightly, if at all, unimpaired. No cause, up to the present, has been discovered for this uncertain behaviour of stored lymph. It is probably due to the
