IMMUNITY AND ANTITOXINS 



261 



living organisms can be weakened, or, as we say, attenuated, 

 by various means. Dead cultures have not been much used 

 to produce immunity except by Pfeiffer. In actual practice 

 the third method is much the most general, viz., filtering a 

 fluid culture free from the bacteria, and then inoculating 

 this in ever-increasing doses. The preparation of diphtheria 

 antitoxin may be taken as an example, but what follows 

 would be equally applicable to other diseases, such as tetanus. 



1. To Obtain the Toxin. First grow a pure culture of the 

 Klebs-Loffler bacillus of diphtheria in large flasks contain- 

 ing " Loffler's medium," or a solution made by mixing 

 three parts of blood serum with one of beef broth and add- 

 ing one per cent, of common salt (Na CI) and one per cent, 

 of peptone. An alkaline medium is preferable. The flask 

 was thoroughly sterilised before use, and is 



now plugged with sterile cotton-wool and in- 

 cubated at J']'' C. for three or four weeks. 

 Pure air may be passed over the culture 

 periodically, thereby aiding the growth. 

 After the lapse of about a month a scum of 

 diphtheria growth will have appeared 

 over the surface of the fluid. This is 

 now filtered into sterilised flasks, and 

 some favourable antiseptic added to 

 ensure that nothing foreign to the 

 toxin shall flourish, and the flasks are 

 kept in the dark. Here, then, we 

 have the product, the toxin, ready for injection into the horse. 



2. Immunisation of the Horse, It is evident that only 

 healthy horses are of service in providing healthy antitoxin, 

 even as healthy children are necessary in arm-to-arm vacci- 

 nation. To provide against any serious taint the horse is 

 tested for glanders (with mallein) and for tuberculosis (with 

 tuberculin). The dose of the injection of toxin is at the 

 commencement about -^ cc, or a little more. The site of 



Flask used for the Preparation of 

 the Toxin of Diphtheria 



