72 INFECTION AND RESISTANCE 



Mechanical trituration is also the principle of the production of 

 the new tuberculins as advised by Koch. 



One of the earliest methods of obtaining bacterial substances 

 by mechanical means was that used by Buchner and Hahn 39 in the 

 production of their "plasmines." The bacteria were grown in quan- 

 tity on large agar surfaces, the moist bacterial masses triturated 

 together with quartz and were then subjected to high pressure in an 

 especially constructed press spoken of as the "Buchner press." 



Mechanical breaking up and extraction of the bacteria also under- 

 lies in principle the use of the variously constructed shaking ma- 

 chines. There are many models of such machines on the market, all 

 of them designed to accomplish prolonged agitation of bacterial emul- 

 sions. In many cases the apparatus can be placed inside of an incu- 

 bator and shaking carried on at 37.5 C. The bacteria are suspended 

 for this purpose in distilled water salt solution, weak alkali, or in 

 serum, and glass beads or sand may be added to aid in their mechan- 

 ical injury. Shaking must be continued for 24 hours or more in 

 order to give good results. 



IV. ACTIVE IMMUNIZATION WITH BACTERIAL PRODUCTS ( TOXINS) 



As soon as the investigations of Roux and Yersin had shown that 

 in some diseases, at least, the injury sustained by the infected animal 

 was largely due to the soluble toxins produced by the bacteria, it 

 was logical to attempt to immunize animals with such products. 

 Probably the first attempts in this direction were those made by 

 Salmon and Smith in hog cholera. The experiments of these writers 

 have attained much historical importance since they represent the 

 first purposeful attempt to immunize animals with the products of 

 bacterial metabolism. In the actual experiment, however, the im- 

 munization practiced by Salmon and Smith was probably a combina- 

 tion of immunization by bacterial products and by dead bacteria. 

 Nevertheless, the thought of immunization with bacterial products 

 was the underlying one in their experiments. Working with the 

 hog cholera bacillus which they had recently discovered they im- 

 munized pigeons in the following way: The bacilli were grown in 

 broth for two weeks, and the cultures were killed by exposure to 58 

 to 60 C. for several hours. One and one-fifth cubic centimeter of 

 this culture liquid was then injected into pigeons, and after three 

 such injections the inoculated pigeons withstood, without harm, doses 

 of the bacilli which rapidly killed untreated animals. Salmon and 

 Smith 40 stated distinctly in their conclusions that : "Immunity may 



39 Buchner and Hahn. Munch, med. Woch., 1897. 



40 Salmon and Smith on "A New Method of Producing Immunity from 

 Contagious Disease," Proc. Biol Soc., Wash., D. C., Ill, 1884, 6, p. 29, 

 printed Feb. 22, 1886. 



