574 PATHOGENIC MICROORGANISMS 



point, the toxin remains stable for long periods. Electrical currents 

 passed through toxic broth have little or no effect upon it. 



Epidemiology of Diphtheria. 33 There is no disease in which 

 sanitary control can accomplish so much as in diphtheria because we 

 are furnished in this instance not only with accurate and simple methods 

 of bacteriological diagnosis, of cases and carriers, but we have available 

 a specific susceptibility test by means of which we can pick out the 

 susceptibles in any group, as well as methods of prophylactic protection 

 which allow a choice between a speedy and a slow procedure, both of 

 them of proven value. In this disease, sanitary measures have made 

 tremendous strides and greatly reduced both morbidity and death 

 rate since the introduction of bacteriological methods. Newsholm 34 

 has studied death rates in diphtheria, and found that in earlier years, 

 great epidemics of diphtheria used to spread through the great cities. 

 There was such an epidemic in London in 1874. In 1872 he states that 

 the death rate from diphtheria and croup in Boston was 35 per 100,000, 

 but in 1881, it was close to 218 per 100,000. Epidemic waves seem to 

 have recurred at five- and ten-year intervals, but even in the inter- 

 epidemic years in cities generally, the death rate seems to have ranged 

 anywhere from 20 to 60 per 100,000. It was, and is always endemic 

 all over the world, is somewhat more prevalent in colder climates where 

 upper respiratory inflammations are more common, and, for some 

 unknown reason, has been relatively more common in rural than in 

 urban communities. Quite naturally, the disease has always been 

 particularly a school disease among children. From studies by Schick, 35 

 Hahn, 36 and others, it appears that the new-born child is endowed with a 

 certain amount of diphtheria antitoxin by the mother, probably through 

 the placenta, to some degree perhaps transmitted through the colos- 

 trum. This relative immunity fades at the end of the first year of life 

 and is gradually reacquired so that the most susceptible years are 

 between one and perhaps nine or ten years of age. In the army, with 

 an age group ranging from twenty to thirty years, it was found, during 

 the recent war, that about 10 per cent of the personnel was Schick 

 positive or, therefore, susceptible. For more accurate susceptibility 

 statistics we must await more extensive measurements and statistical 

 studies of Schick tests. 



33 See Zinsser, Nelson ; s Loose-Leaf Medicine, 9, 205. 

 Newsholm, Epidemic Diphtheria, London, 1898. 

 35 ScMck, Ueber Diphtherimmunitat., Wiesbaden, 1910. 

 "Hahn, Dent, mcd. Woch., 38, 1912, 1366. 



