88 CLINICAL BACTERIOLOGY AND 



The animal is then inoculated with a dose of attenuated 

 toxin prepared by heating the virulent poison or by treat- 

 ing it with a chemical agent, either of which will reduce 

 its strength. Repeated inoculations should be followed up, 

 at stated intervals, with increasingly virulent doses. 



The toxins which are injected are prepared by growing 

 the specific bacteria upon suitable fluid media. The cultures 

 are then passed through a Pasteur-Chamberland filter, or a 

 similar filter, to remove the bodies of the bacteria. 



When a sufficient degree of immunity has been reached, 

 and three or four days have elapsed after giving the last 

 dose of toxin, the blood is withdrawn under aseptic pre- 

 cautions from the jugular vein by a sterile cannula, and 

 collected in sterile vessels. These are put aside, preferably 

 on ice, to allow the blood to clot, and in due course the 

 serum is decanted into sterile stock bottles, a small quantity 

 of preserving {antiseptic added, and they are ready for 

 use. 



Antibacterial serums are produced in a similar manner, 

 but the actual bacteria themselves are injected instead of 

 their toxins. Before a degree of tolerance is reached, the 

 dead bodies of the bacteria or an attenuated culture are 

 given at the outset, or a dose of antitoxic serum is ad- 

 ministered to mitigate the effects of the first virulent dose. 



All serums should be tested before using, to see that they 

 are free from bacterial contamination, by flooding some upon 

 a culture medium and incubating, and to insure non- toxicity 

 the serum should be injected into a small animal first. 



Serums are standardized by the physiological test. An 

 animal is taken which reacts in a constant manner to the 

 poison, and dying within a certain time. It is known that 

 a given quantity of poison will destroy an animal of a given 

 weight in a given time. This is taken as a standard. It 

 is then necessary to find what amount of antitoxin is re- 

 quired to neutralize this dose, and we find equal quantities 

 of a given antitoxin will do this, a standard thus being 

 set up. 



