DIPHTHERIA TRANSMISSION 281 



animal in type, rendered immense aid to medicine 

 in making the diagnoses of infectious diseases more 

 certain, and elucidating the processes, which occur 

 in patients suffering from them, but they have 

 widened the very narrow views previously held. 

 We now know that an individual infected with a 

 certain disease-producing microorganism, for ex- 

 ample the diphtheria bacillus, may exhibit a great 

 variety of symptoms. He may suffer from the 

 disease in an acute form and die in a few hours or 

 days, or he may suffer from the disease in a subacute 

 or mild form, showing the typical symptoms in a 

 lesser degree. Such conditions are easily recogniz- 

 able and give rise to few difficulties in diagnosis. 

 The patients are isolated, and at least for a time 

 are prevented from spreading the disease. Many 

 individuals, who become infected, exhibit symptoms 

 which are less easily recognizable, such as mild sore 

 throats, nasal catarrh, etc., while others, though 

 harbouring the bacilli, remain in perfect health. 

 Such persons are known as ' carriers,' and are of the 

 greatest importance. They can be recognized only 

 by bacteriological examination, and frequently 

 remain undetected, and go about unconsciously 

 spreading infection. Further, those who have re- 

 covered from the disease in its recognizable forms 

 frequently harbour the bacilli for long periods and 

 disseminate infection as do the carriers. Every 

 infectious disease has its typical, atypical, mild 

 cases, and carriers, and it is on the recognition of 



