648 MICROBIOLOGY OF THE DISEASES OF MAN AND ANIMALS. 



DISEASES OF UNKNOWN CAUSE.* 



SCARLET FEVER, MEASLES, GERMAN MEASLES, DUKES DISEASE, 

 SMALLPOX, CHICKENPOX, MUMPS. f 



These diseases constitute a group the actual biological causes of 

 \vhich are unknown, yet which show analogies to diseases, the causes of 

 which are known, so close as to make tenable the hypothesis that they 

 are due to similar causes. 



Mumps is in a class by itself, its characteristics, well known to the 

 laity, marking it off from the others sharply. Like the others it is infec- 

 tious; it is derived only from a preceding case; it has a more or less definite 

 incubation period (i.e. an interval between the date of infection and the 

 first development of symptoms, during which ordinary health is enjoyed), 

 and a prodromal stage (i.e. a period in which fever, headache, and other 

 more or less marked constitutional symptoms exist without any marked 

 characteristic symptom). Then appears the swelling of the parotid 

 salivary glands just in front of the ears with some pain. The symptoms 

 usually amend after a few days and the patient goes on to full recovery. 

 There is no rash nor any great disturbance of the intestinal tract or 

 internal organs. 



Smallpox and chickenpox together form a group quite often confused 

 clinically, especially in the early stages and especially when smallpox 

 is prevalent in mild form. They have incubation periods, averaging 

 about twelve days, in smallpox varying little from this period, in chickenpox 

 varying widely from it. Smallpox has rather severe prodromes, backache, 

 headache, fever, and sorethroat, the rash appearing on the third or fourth 

 day. Chickenpox usually has light or no prodromes, the rash ap- 

 pearing on the same day or within twenty-four hours, as a rule. In 

 both diseases the face, chest, back, arms, hands, legs, and feet are likely 

 to show eruption, but chickenpox tends to show the greatest number 

 of spots "under cover," i.e. on the parts usually covered by clothing, 

 while smallpox tends to show the majority upon the face, neck, arms, 

 wrists, and hands, rather than on the body. The skin lesions themselves 

 differ very markedly, the typical lesions of chickenpox being superficial, 

 thin-walled, high, rounded, and filled with clear liquid, those of smallpox 



* Arranged alphabetically except group of diseases placed first. 

 t Prepared by H. W. Hill. 



