24 8 SCIENCE PROGRESS 



is of the utmost value. More recently, even in the graver 

 general infections — the septicaemias — by actual bacteriological 

 examination of the blood obtained by venesection it is possible 

 to determine what bacterium is the cause of offence in each 

 case. 



Further, inferential diagnosis may be made by the examina- 

 tion of the blood serum or lymph — as, for instance, by means 

 of the Widal-Grunbaum test. It will be seen later that the 

 examination of the blood serum, lymph, effusion, etc., as regards 

 their opsonic power, may also be of great value in this con- 

 nection. 



(2) The Vaccine. — The therapeutic agent is a vaccine — the 

 bacterium in the suspension being the one corresponding to the 

 causative agent of the disease under treatment. If necessary — 

 and this is so in many cases, especially when dealing with 

 bacteria of the Colon group and the Streptococci— the vaccine 

 may be prepared from the actual offending bacteria. Cultures 

 taken from the site of infection are made on a suitable medium, 

 and the resulting growth is washed off and suspended in 

 normal salt solution. This emulsion is then poured into a test 

 tube, hermetically sealed off in the flame, and then sterilised by 

 heat. The temperature employed must be sufficient to kill the 

 bacteria, but only just sufficient for this purpose, an important 

 consideration in the preparation of a vaccine being to alter as 

 little as possible the chemical composition of the bacterial 

 protoplasm. In the case of most of the commoner pathogenic 

 bacteria a temperature of 6o° C. for one hour is enough. A 

 water bath is the form of steriliser employed. After sterilisa- 

 tion some of the vaccine is withdrawn, planted out on culture 

 media, and incubated for 24 hours. If these media remain sterile 

 at the end of this time the vaccine may be regarded as sterile, 

 though for precaution against subsequent contamination | per 

 cent, of Lysol or some such antiseptic is added. 



(3) Before giving the inoculation it is essential to know how 

 much is being given, and for this reason the vaccine has to be 

 standardised. This is accomplished by counting the number of 

 bacteria in the emulsion we have made. At first this seems 

 almost impossible, but Wright has practically solved the diffi- 

 culty in this way. " Availing himself of the fact that the normal 

 blood contains about 5,000,000 red cells per cubic millimetre (the 

 actual number can, of course, be determined by making a red 



