448 Biology in America 



a weakened (smallpox) or dead virus (typhoid fever) ; the 

 efficiency of anti-toxins in diphtheria, and tetanus depends 

 upon the latter, while meningitis serum acts both as a means 

 of destroying the meningitis bacterium and of neutralizing 

 the toxin produced by it. 



But to return to the discovery of a cure for meningitis. 

 For several years experimenters had been attempting to 

 .render animals immune to the disease, and then by injecting 

 some of their blood serum into other animals to make these 

 latter immune in their turn. Various species of animals 

 were employed for this purpose, but the horse was the one 

 finally selected, partly because normal horse serum, when 

 injected into human beings produces no ill effects, and, partly 

 for the reason that the horse is readily immunized against 

 meningitis, and partly because of the large amount of serum 

 obtainable from one animal. In immunizing a horse the first 

 step is to secure the bacteria from some victim of the disease 

 and grow them on some culture medium such as agar impreg- 

 nated with beef bouillon and other nutrient materials. After 

 a good growth has been obtained, the culture is scraped off 

 from the agar and heated to 55 or 60 C. in physiological 

 salt solution, to destroy the bacteria. A drop or two of this 

 solution, containing the dead bacteria and some of their prod- 

 ucts, is then injected into a horse which has been kept under 

 observation for some time and rigorously examined to deter- 

 mine its healthfulness. After eight days a second and larger 

 dose is given and this is repeated at similar intervals for 

 periods of from four months to a year, until the horse can 

 withstand large injections, not of dead, but of living bacteria. 

 The horse is then bled under aseptic conditions and the 

 serum so obtained put in sterile vials and sent out to 

 physicians for use. 



The treatment with this serum was not at first successful 

 however. The world-wide epidemic of cerebro-spinal menin- 

 gitis beginning in 1904 stimulated the search for a remedy 

 and these experiments were soon successful. The credit for 

 the first successful use of anti-meningitis serum probably 

 belongs to a European Jochmann, but the principal devel- 

 opment of the method is due to Flexner, working at the 

 Rockefeller Institute in New York. 



Early in his experiments Flexner employed monkeys as 

 more likely than the lower animals to react to human diseases 

 in a manner similar to men. By injecting cultures of the 

 meningitis bacterium into the spinal column of monkeys Flex- 

 ner infected them with the disease. Following these experi- 

 ments he similarly employed intra-spinal injections of the 

 curative serum, at first on monkeys and later on man, with 



