CHANNELS OF INFECTION 289 



experiments in so far as they yielded positive results, were also 

 open to the same unreliability. Unfortunately too there was, on 

 the other hand, circumstantial evidence of various kinds, which, 

 while it proved little, opened up a variety of possibilities by which 

 the milk consumed in London might have become infected. 



Such are the main facts on both sides of this matter. We have 

 quoted the main facts respecting this epidemic, not on account of 

 its conclusions, but because it was one which contains so many, and 

 so varied, instructive lessons on the whole question of milk 

 epidemiolog>'. It opened up new ground. It brought into 

 prominence the intimate relationship existing between the in- 

 fectious diseases of animals and similar diseases in man. But 

 after an examination of the evidence on both sides of the question 

 we are of opinion that the case for cow scarlatina was not proved. 



Channels of Infection in Scarlet Fever 



Scarlet fever is disseminated in many ways from person to 

 person, and also by the vehicle of " fomites." The virus is not 

 diffusible, but is evidently tenacious of life. Infected garments 

 that have been put aside for months have been known to originate 

 an outbreak of the disease. Linen has been known on many 

 occasions to infect laundresses. There is no evidence that the 

 virus can be conveyed by water. As a rule, probably the infection 

 of scarlet fever is not greatly spread by aerial connection, but by 

 articles (toys, books, bed-clothes, letters, etc.), and such infected 

 articles if set aside in stagnant air, at a moderate temperature, and 

 in the absence of daylight, may retain the infection, like garments, 

 for months. 



Infectivity begins at the earliest stage of the attack, but is 

 probably greatest when the fever is at its highest. In most cases 

 the patient is free from infection at the end of six weeks. There 

 is now strong evidence that at least the later desquamation is not 

 infective. Probably the infection lingers longest in the nasal, 

 tonsillar, buccal, and pharyngeal mucus, and especially in any 

 chronic discharge from those mucous membranes. Discharges 

 from the ear may retain infection for months.^ 



It is most probable that milk obtains its infection of scarlet 

 fever from being brought into contact with persons suffering, as a 

 rule, from the early and acute stages of the disease, when the skin 



' See also Report to Metropolitan Asylum Board on Return Cases of Scarlet 

 Fe7>er, by W. J. Simpson, M.D., 1901, p. 24 ; also Brit. Med. Jour., 1902, voL 

 ii., p. 445 (M. H. Gordon). 



T 



