TYPHOID FEVER. 385 



3. The dilution of the known quantity of blood con- 

 tained in the tube with a measured quantity of the 

 bouillon, or diluted agar-agar, culture of the bacillus. 



The standard tube that I adopted had a diameter 

 about equal to the K string of a violin. A larger or 

 smaller tube would have done quite as well. In such a 

 tube the column of blood rises about an inch and weighs 

 about 0.018 gram. As personal equation in judging 

 size is a marked source of error, the experimenter must 

 work out his own standard tube and not adopt that which 

 has just been given. It is important to know the length 

 of the column that has a certain weight, because, as each 

 tube is not separately measured and graduated, the two 

 chief means of avoiding error will be (i) to have the 

 tubes as nearly as possible of equal diameter, and (2) to 

 prove them to be so by observing that the columns of 

 fluid they contain when used are of the same length, re- 

 jecting one after another all the tubes which seem to 

 the eye to have the proper caliber, but in which the 

 column is obviously longer or shorter than that of the 

 original tube. 



Keeping the standard tube before him as a guide, and 

 using a Bunsen flame which is better than a blowpipe, 

 because it does not heat the glass so rapidly and make it 

 so soft the experimenter prepares one hundred or more 

 capillary tubes as nearly as possible of the same size as 

 that of the standardized tube. All the irregular sizes 

 are rejected, and the suitable sizes cut into portions 

 about three inches long. These pieces, which should 

 number several hundred (it is economy to make a large 

 number at a time), are now carefully sorted, being com- 

 pared with the standard tube at both ends, and thrown 

 away if too large or too small at either. It is best to 

 sort the tubes twice on different days, or have several 

 different persons go over them all. Of course, some 

 tubes of quite different caliber will, in spite of all pre- 

 cautions, remain in the bundle, but this is no serious 

 matter, because at the last moment the height of the 



25 



