224 INFECTION AND IMMUNITY 



infectious agent, or germ, is attached, and which 

 may retain its infecting power for many months. 

 The sputa of scarlet fever patients also contains the 

 germ and by some physicians is believed to be to a 

 large extent responsible for the spread of the dis- 

 ease. As the mucous membrane of the mouth and 

 throat is involved in the eruption which is character- 

 istic of the disease and is in fact the locality where 

 this eruption, followed by desquamation of the epi- 

 thelium, may first be observed, it is evident that all 

 expectorated material must contain the infectious 

 agent. The disease may be communicated by the 

 scarlet fever patient at any time during the period of 

 desquamation, which may last for a month, or more. 

 The period during which the patient should be isol- 

 ated, dating from the outset of the attack, is gen- 

 erally fixed at six weeks. The infection may persist 

 in clothing and bedding, in use during the period of 

 desquamation, or exposed in the sick-room, for a 

 year or more. 



Certain persons seem to have a natural immunity 

 to scarlet fever and escape the disease although re- 

 peatedly exposed to it. In some instances, no doubt, 

 this failure to contract the disease is due to a pre- 

 vious mild and unrecognised attack rather than to an 

 inherited immunity. The protection afforded by an 

 attack of the disease, however mild, is almost abso- 



