INTRODUCTION 



THE history of immunology as a science is distinctly modern and 

 in the investigation of details dates back only as far as the time of 

 Louis Pasteur. Jenner's work on smallpox vaccination represents 

 most painstaking and thorough investigation; it was epochal in 

 character, and of the utmost importance in practical results, but was 

 not immediately followed by any general application to other dis- 

 eases, probably because of the limitations of technical methods. 

 Observations of the phenomena of immunity were, however, made 

 in ancient times and the resistance to second attacks of such dis- 

 eases as measles, scarlatina, variola, varicella must have been com- 

 mon knowledge from the earliest days of the human race. Whilst 

 many of the earlier students of medicine recognized a certain simi- 

 larity between poisoning and infectious disease, yet Hippocrates 

 could see no such resemblance and his theory of the four humors 

 was dominant throughout the Middle Ages. With minor exceptions 

 this belief held sway until well into the Renaissance. In 1548, how- 

 ever, Fracastore proposed the theory that infection was carried 

 from person to person " per contactum " or " per fomites," and from 

 this time dates real progress in the investigation of infectious dis- 

 ease. This led subsequently to the establishment of two schools of 

 thought, the one believing disease to be due to substances of basic 

 or acid principle, and the other believing disease to be due to para- 

 sites. The development of the latter idea was forced to await the 

 discovery of means to view minute parasites and, as a matter of 

 fact, was delayed much longer, because the invention of the micro- 

 scope by Kircher in 1659 and van Leeuwenhoek in 1675 far ante- 

 dated the connection now established between minute parasites and 

 infectious disease. Nevertheless, Plenciz in 1762 expressed a belief 

 in the direct etiological connection between certain forms of disease 

 and microorganisms, and established the conception of the " con- 

 tagium vivum." This idea was revived by Henle and by 

 Brettoneau, but attracted no permanent attention. 



As perhaps the first observation leading up to our present con- 

 ception of infectious diseases, and therefore to immunity against 

 them, was the discovery in 1837 by Schwann that certain forms of 

 fermentation are due to the presence of yeasts, an observation made 

 at about the same time by Cagniard-Latour. Although at this time 

 there was little, if any, thought that this discovery had any impor- 

 tant bearing on infectious disease, yet within the succeeding decade 

 favus, thrush, and pityriasis versicolor had been demonstrated to be 

 due to specific fungi. Nevertheless, the possible similarity of fer- 

 mentation and infectious disease had been considered in a more or 

 less philosophical way, and Robert Boyle had said : " He that thor- 



xiii 



