110 IMMUNOLOGY 



Kuttner and Katner (1923) confirmed the observation of other 

 investigators who found that diphtheria antitoxin passes through 

 the human placenta from mother to child but that it is not present 

 in the colostrum or breast milk of the mother. Kuttner and Ratner 

 call attention to the anatomical variations of the placenta in dif- 

 ferent animals. There are four main types of plncentas: those 

 with one, two, three, or iowr cell partitions or layers between the 

 fetal and maternal blood. In man and rodents there is only one 

 connective tissue layer while ruminants have three and other an- 

 imals such as swine have four layers. 



Acquired Immunity. — It is now generally recognized that indi- 

 viduals recovering from certain acute infectious diseases such as 

 typhoid fever, scarlet fever, measles, mumps, poliomyelitis and 

 smallpox develop a lasting specific immunity as a result of the in- 

 fection. To a certain extent this is true also of tuberculosis. In 

 the case of syphilis the patient is immune to reinfection with 

 Treponema pallidum so long as he lias syphilis, but loses his im- 

 munity after he has been cured of the disease. Individuals who 

 recover from influenza or pneumonia or from various pyogenic in- 

 fections owe their recovery to the operation of immunity mech- 

 anisms but their increased resistance is of short duration. 



The exact mechanism of acquired immunity is not clearly under- 

 stood. While antibodies are of some importance in resistance, it 

 has been established that a correlation between antibody titer and 

 resistance does not always exist. Hadfield and Garrod (1939) 

 state that the development of lobar pneumonia seems to re- 

 quire a pre-existing humoral immunity ; Coriell and Sher- 

 Avood (1940) found no virucidal antibodies in cats that were 

 immune to vaccine virus highly virulent for rabbits ; Kessel and 

 Stimpect (1941) studied poliomyelitis in a large series of monkeys 

 and compared immunity with antibody titer. They found a very 

 definite lack of correlation since it was present in only 50 per 

 cent of their convalescent monkeys. Further consideration of im- 

 munity mechanisms will be presented in later chapters. 



Immunization Against Viruses and Rickettsiae. — The phe- 

 nomenon of acquired resistance or active immunity to infection 

 was perhaps first observed by the Chinese. They practiced nasal 

 inoculation of smallpox virus and the production of the disease 



