MICROBIAL DISEASES OF MAN AND DOMESTIC ANIMALS 855 



lesions of chickenpox being superficial, thin walled, high, rounded, 

 and filled with clear liquid, those of smallpox being deep seated, tense, 

 opaque, with a tough covering of epithelium. There are many other 

 points of distinction, and any one familiar with the two diseases can 

 hardly fall into error when dealing with typical cases at whatever stage 

 they are encountered. To the layman's eye, however, the two are 

 often indistinguishable. 



Scarlet fever, measles, German measles, and Duke's disease are often 

 likewise confused by the laity and even by physicians who have not 

 had opportunities for extensive study. 



German measles is clinically related to true measles somewhat as 

 chickenpox is to smallpox, i.e., they are wholly distinct diseases yet 

 show characteristics easily confused on superficial consideration. 

 Duke's disease is perhaps not a distinct entity; much has been said on 

 this point and a satisfactory decision will probably never be reached 

 until the causative agents have been found. It may be described 

 briefly for clinical purposes as a variety of German measles having a 

 scarlatiniform instead of a measly rash. 



Scarlet fever has an average incubation period of about five days, 

 or perhaps sometimes less. The prodromes are those usual to all 

 these infections headache, fever, and sore throat, but the latter 

 is especially severe. Within twenty-four hours the rash appears usually 

 on the chest first, a bright scarlet superficial punctate flush, extending 

 rapidly over the body. 



In measles the incubation period is longer, averaging nine or ten 

 days, almost without any variation. The prodromes, headache, fever, 

 and sore throat, are accompanied by very marked coryza and photo- 

 phobia, catarrh and "cold on the chest." 



The rash appears about the fourth day, appearing on the face and 

 back but rapidly extending. It is darker, bluer, and deeper than the 

 scarlet fever rash and unlike the latter is palpable. Koplik's spots 

 appear on the buccal membrane early in the disease. 



In German measles the prodromes are so indefinite that it is difficult 

 to determine their length; very commonly the rash is the first thing no- 

 ticed. It appears on the face, chest, back, and arms as a light sub- 

 cuticular mottling (measles type) or a more uniform pink flush (scarla- 

 tiniform or Duke's type) ; with this rash the eyes show some injection 

 and slight photophobia develops. The attack passes off quickly, 

 without complications. 



