VACCINE-THERAPY 75 



view as much as possible. That the field may be divided 

 into squares to facilitate counting, we take a cover-glass and 

 mark cross-lines on it with a pen and ink, or four hairs 

 crossed and stuck on it with seccotine will answer our 

 purpose, and dropped on to the diaphragm of the eyepiece. 

 We now take a pencil, and count in each square the 

 number of bacteria in one column, and in the other the 

 number of red corpuscles. The stage is moved, and 

 another square counted, and so on, until we get a total of 

 500 red cells. 



Sometimes we find a square contains an excess of bundles 

 or chains, or the elements may be badly stained and set 

 out. It is then better to pass on to another square, and 

 estimate from that. The two columns now total 500 red 

 corpuscles as against, for example, 640 bacteria; the ratio 

 is therefore 500 to 640. We know that there are 5,000,000 

 red cells in a cubic millimetre of blood. Since equal 

 volumes of blood and emulsion have been taken, 1 cubic 

 millimetre of emulsion will contain — 



5^000,00^640 = 6400000 . 

 500 ' ' 



But 1 c.c. contains 1,000 cubic millimetres; therefore the 

 emulsion contains 6,400,000 x 1,000 = 6,400,000,000 bac- 

 teria per cubic centimetre, and by a process of dilution any 

 suitable strength can be obtained. Now we desire to make 

 our vaccine for future use. The bottles used for storing 

 purposes are rubber-capped, 25 and 50 c.c. capacity, 

 sterilized and filled with £ per cent, carbolic and NaCl 

 (0 - 85 per cent.) solution; and we wish every cubic centi- 

 metre to contain 1,000,000,000 devitalized bacteria, there- 

 fore in our 50 c.c. we must put 50,000,000,000 bacteria, and 

 as we have already seen every cubic centimetre of our 

 emulsion contains 6,400,000,000 bacteria, it is simply a 

 question of dividing the greater amount by the lesser : 



50,000 million = ? . gl ( W)< 

 6,400 million v ' 



