384 PATHOGENIC BACTERIA. 



In the absence of a satisfactory method of securing 

 definite small quantities of blood for immediate or sub- 

 sequent use, I was led to make some experiments with 

 capillary tubes to determine their possible value for the 

 purpose. 



It is a well-known physical phenomenon that in clean 

 capillary tubes fluids are attracted to a height varying 

 according to the diameter of the tube and the density of 

 the fluid. In tubes of equal diameter the height of the 

 column is invariably the same. 



Such tubes can be made by heating a piece of ordinary 

 glass tubing, such as is to be found in every laboratory, 

 in a Bunsen flame for a few minutes until it becomes red 

 and soft, removing the glass from the flame, and then 

 pulling upon the ends steadily and slowly until the tube 

 is drawn out to the desired diameter. The errors to be 

 avoided in making the tubes will be heating too much 

 and making the glass too soft, drawing out the tube 

 while still in the flame, and drawing too rapidly. The 

 result of these erroneous methods will be that the tubes 

 are much shorter and finer than is desired. A few mo- 

 ments' practice will show just how the manipulation 

 should be done to secure the best results. 



The fact was, however, established that tubes of about 

 the same diameter showed almost no variation in the 

 quantity of liquid contained. So little was the difference 

 in the length of the column and the weight of the con- 

 tained blood in tubes recognized by the eye to have uni- 

 form caliber that I have no hesitation in recommend- 

 ing an application of the capillary tube for securing 

 small measured quantities of blood for the specific typhoid 

 tests and similar experiments. 



The application of the method is simple and consists in: 



1. Accurately weighing the amount of blood that 

 enters a capillary tube of a size arbitrarily selected as a 

 standard. 



2. The manufacture of a large number of tubes of the 

 same size. 



