76 APPLIED IMMUNOLOGY 



(3) Employment of dried blood: Two or three 

 drops of patient's blood are collected upon a clean 

 glass slide or non-absorbent paper and allowed to dry 

 there. In making the dilution, enough water is added 

 to the dried blood to replace that lost in drying, and 

 the clot well broken up in it by means of a platinum 

 needle. The dilution can then be made by drops from 

 a capillary pipette as described above. This method 

 is useful in cases where the necessary apparatus for 

 either of the other two methods is not at hand, and 

 where the blood has to be sent for examination a dis- 

 tance. While the matter of dilution by this means is 

 largely guesswork, reliable results can be obtained 

 from it, though if possible it is better to use one of the 

 other methods above described. 



{b) Preparation of the Culture of Typhoid 

 Bacilli. — A stock agar culture of typhoid bacilli should 

 be kept at hand, and should be renewed by transfer- 

 ring to a fresh agar tube every three or four months. 

 For use in the test a bouillon culture is made from this. 

 The bouillon culture should be 24 to 48 hours old, 

 grown at room temperature. In such a culture the 

 typhoid bacilli are found to be present in sufficient 

 numbers, of large size, and very motile. A satisfac- 

 tory bouillon culture can be kept constantly on hand 

 by inoculating a fresh tube with the preceding one 

 every 48 hours. If the bacilli die out or prove other- 



