IMMUNOLOGY 9 



Some of the phenomena of natural acquired immunity were of 

 course famiUar even to the ancients, and people have practiced 

 for centuries exposing themselves to diseases at convenient times 

 in order to acquire subsequent immunity. Jenner in 1797 

 devised vaccination with cowpox to give immunity to smallpox. 

 It was not until 1880 and 1881 that Pasteur discovered the 

 possibility of producing immunity by inoculation of germs arti- 

 ficially rendered harmless or relatively harmless, or by the inocu- 

 lation of the strained excretions of the bacteria as they exist in 

 pure cultures. 



From Pasteur's epoch-making discoveries has arisen in the 

 last 25 years the science of immunology. Although up to the 

 present time the successful use of vaccinations or inoculations 

 for cure of, or protection from, disease germs has been applied 

 chiefly to bacterial diseases, the same principles of immunity 

 apply to diseases caused by animal parasites and we may con- 

 fidently expect in the not distant future a great extension of this 

 relatively new field of medicine to diseases caused by animal 

 parasites. It has already been applied successfully to some 

 spirochaete diseases, and to some trypanosome diseases. The 

 difficulty of growing many animal parasites in cultures has largely 

 held back progress along this line, and it is only recently that 

 much advancement has been made. Only a few years ago 

 culturability and non-culturability were believed to be dis- 

 tinguishing characteristics between bacteria and Protozoa. 

 Although methods for growing pure cultures of bacteria arti- 

 ficially were devised and used by Pasteur in 1858, and greatly 

 improved by Robert Koch 15 or 20 years later, it was not until 

 1903 that the artificial cultivation of trypanosomes was ac- 

 complished by two American workers, Novy and MacNeal. 

 In 1905 Rogers in India succeeded in cultivating the Leishman 

 bodies of kala-azar, and thus established their relationship to 

 certain flagellated parasites of invertebrate animals. Since then 

 other investigators have succeeded in the cultivation of other 

 parasitic protozoans, the latest important accomplishment along 

 this line being the successful cultivation of spirochsetes by 

 Noguchi in 1910-12, and of malarial parasites by Bass and Johns 

 in 1913. As yet no pathogenic amebse have been successfully 

 cultured, probably due to their dependence on the presence and 

 action of certain kinds of bacteria. 



