CHAPTER XXII. 



VACCINATION. 



Natural Immunity Ingrafting of Small-pox Jenner's Discovery Klebs 

 -Pasteur Chauveau Grawitz's Theory Buchner's Theory Met- 

 schnikoff s Work Greenfield's Observations on Anthrax Toussaint's 

 Vaccinal Fluid Pasteur's Classical Experiments Other Methods of 

 Diminishing Virulence Chauveau's Soluble Poison Experiments 

 Protection by Alkaloids, Albumoses and Toxalbumens Saprophytic 

 " Anthrax " Hueppe and Wood Antagonism by Blue-pus Products 

 Immunity not the same as Antagonism Summative Action of 

 Bacteria. 



IT has long been recognized that in a number of infective 

 diseases, one attack confers a certain immunity against 

 that special disease in the future. This protective influ- 

 ence may last for a very considerable period, or there may 

 be merely a temporary immunity. It was early noticed, 

 however, that the severity of the primary attack of the disease 

 appeared to bear no very definite relation to the degree of 

 immunity acquired by the patients, although immunity of 

 an animal usually bears a very direct relation to the strength 

 of the vaccine which it has withstood. In fact every degree 

 of immunity may be produced, though this does not always 

 correspond with the severity of the symptoms. Immunity 

 appears to be governed by no very regular laws, for it 

 is found that even in the same species, individuals may 

 differ very considerably as regards susceptibility to first 

 or subsequent attacks of some of the infective diseases. It 

 is known, for example, that whilst certain people have 

 never more than a single attack of measles, others may 

 have several, and that similarly, certain individuals are 

 specially liable to the recurrence of scarlatina, suffering 

 no fewer than three, four, or even more attacks. When 

 differences of species are taken into account these differences 

 of susceptibility are even more marked ; thus sheep and 

 cattle are protected against subsequent attacks of anthrax by 



