230 The Vaccine Institute, Belgaum.
carrying over to the next tube. Where more than one lymph number is dealt with at the same time, an empty tube intervenes. The temperature of the chest is important and great care should be taken to see that the correct temperature is maintained. The chloroform vapour should be passed while the interior of the chest and tubes are at 20° C. ; at this temperature the chloroform acts in such a way that a passage of vapour through the lymph for 20 minutes to half an hour is sufficient to remove most of the extraneous organisms from calf-lymph. Our object is not to remove all the extraneous germs and show no growth on agar plates, when subsequently the lymph is plated out. A few colonies should always remain, and these colonies furnish an accurate indication that the chloroforming has not been pushed so far as to injure the vaccine virus. When all colonies are killed, one cannot be certain that too much chloroform has not been used. If clean plates result from the plating of the chloroformed lymph, then the time of passing the vapour should be reduced, until a small number of colonies, say under 15, are shown on the plates. These few organisms are easily dealt with by the glycerine in the lymph, especially at the temperatures obtaining when the lymph is despatched through the post to the vaccinators in Indian districts. Experience has fully demonstrated that, if some organisms are found in the lymph after chloroforming, the vaccine virus remains uninjured. When the time necessary for passage of chloroform vapour has been determined by this method, such that a few colonies remain alive, as shown on agar plates, the vapour is passed for half that period and the blast pump is then closed and the tubes of lymph are reversed in the chest, so that the first tube becomes the last in the series and the last tube becomes the first. The pump is againt umed on and chloroform passes for the remainder of the time. This method of reversing the tubes prevents the lymph, receiving the vapour first, from being more acted upon than the end of the series, and tends to a uniform purifying process for all the tubes. When chloroform has passed for the correct time the gas-washing bottle is removed and air alone is blown through the lymph, the temperature of the chest being maintained for 10 minutes at 20° C. After this, ice is added to the chest and the temperature is lowered to 10° C. and maintained at this temperature while the air is being blown through. It is found that the passage of air for three hours removes every trace of chloroform from the lymph. The object of keeping the temperature at 20° C. for ten minutes is to prevent the possibility of the chloroform, dissolved in the lymph, condensing out as liquid chloroform, which might occur if the temperature
