MICROBIAL DISEASES OF MAN AND DOMESTIC ANIMALS 8oi 



DISEASES OF UNKNOWN CAUSE* 



Scarlet Fever, Measles, German Measles, Duke's Disease, 

 Smallpox, Chickenpox, Mumps f 



These diseases constitute a group the actual biological causes of 

 which 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 

 infectious; 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 as a rule, 

 although metastases, affecting the mammae, ovaries or testicles de- 

 velop at times; and secondary complications sometimes are found. 



Smallpox and chickenpox together form a gtoup quite often confused 

 clinically, especially in the early stages and especially when smallpox 

 is prevalent in mild form. They have incubation periods, approxi- 

 mating 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 sore throat, the rash appear- 

 ing on the third or fourth day. Chickenpox usually has light or no 

 prodromes, the rash appearing 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, hands, legs and feet rather than on the 

 body. The skin lesions themselves differ very markedly, the typical 

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



• Arranged alphabetically except group of diseases placed first. 

 t Prepared by H. W. Hill. 

 51 



