ground by passing through these machines four times, when a very uniform emulsion is obtained. Each machine is capable of grinding 20 grammes of pulp per hour. The glycerine and water mixture is prepared by mixing the best quality redistilled glycerine with sterile distilled water. The mixture is autoclaved, rendered faintly alkaline with soda bicarb., placed in a flask, which is held in a stand in an inverted position, connected by a 3-way tap to a graduated burette, and measured off into flasks as required. It is important that the lymph emulsion should be kept faintly alkaline, as any development of acidity is detrimental to the vaccine principle. The lymph emulsion, as it leaves the grinding machines, securely corked in suitable glass tubes, is found to contain a large number of extraneous micro-organisms. Ten milligrammes of this lymph, when mixed with agar culture medium and poured on plates, shows an uncountable number of these extraneous germs. They consist, for the most part, of staphylococcus albus, aureus and citreus from the calf's skin and seem to develop in the vaccinia vesicle at the same time as the vaccinia virus. They are not, as a rule, markedly pathogenic but, where crude unpurified lymph is used for vaccination, a number of abscesses are liable to be met with, and the inflammation, accompanying the development of the vaccine vesicle, is much more marked than in the case where lymph is used which has been rendered free from these extraneous organisms. Hence, the desirability of freeing the lymph from these germs. In many Vaccine Institutes, such as that at Hendon, London, reliance is placed on the purifying effect of glycerine, but this is found to be very slow, and may require many months' storage, where the lymph is kept at or below freezing point. Dr. Blaxall5 states, in this connection, that glycerine has no germicidal action of itself, but in conjunction with heat, it is a powerful germicide and this action varies directly with the temperature. Hence, to get the purifying effect of glycerine on the extraneous organisms, it is found necessary to store the lymph at temperatures considerably above freezing point. Blaxall5 showed this very clearly in his work at Hendon.
This method of purification was given a fair trial at Belgaum. I found it very uncertain in action, and a certain proportion of lymphs ontinue to show largo numbers of extraneous germs, necessitating prolonged storage and frequent bacteriological examinations, before the lymphs are pure enough for issue. Unfortunately, prolonged storage frequently reduces the activity of the virus, so that trial on children is advisable before despatch to the districts.
