DISEASES OF UNKNOWN ETIOLOGY 649 
as the rash abated .' SUj2;ht aji^hitinating ])o\ver was observed in several 
cases- but the defjjree of dihition was very low (1 to 2 to 1 to 8). The 
relationship of the organism to the disease is not definitely established. 
Ferry and Fisher^ isolated a streptococcus, producing a green colora- 
tion in blood agar, which, they state, produces a soluble toxin specific 
for measles. 
Convalescent serum, taken from human cases, between the second 
week and third month following recovery, in 5 cc. amounts, is said to 
have prophylactic, and to some degree, curative value. 
The present status of the etiology of measles indicates that the virus 
is present in the nasal secretion, the blood, and possibly the epidermis, 
during the earlier phase of the eruption. Monkeys are moflerately 
susceptible and may be infected with such material successfully.'* 
Rabies. — Rabies is a disease primarily observed among the carni- 
vora— dogs, wolves and cats— but it is transmissible to horses and to 
man. Laboratory animals are readily infected with the virus. The 
saliva of rabid animals is infectious and the natural mode of inocula- 
tion is through the bites of infected animals. The disease is also readily 
transmissible in an experimental way through the injection of emul- 
sions of the cord or brain of rabid animals directly into the central 
nervous system of other animals. The infectious nature of rabies was 
first clearly shown by Pasteur, Chamberland and Roux.^ 
The incubation period for "street rabies" is, on the average, from 
one to two months, but it may be considerably longer. The incidence 
of the disease among those bitten by rabid dogs depends largely upon 
the location of the bite— if upon the body protected with several 
layers of clothing, infection may fail to develop; the virus is held 
back by the clothing and fails to enter the wound. In general the 
inoculation period is shortest when the hands or face are attacked, 
because the virus acts upon the central nervous system and reaches 
it through the peripheral nerves. 
The disease in man is practically always acute and death usually 
terminates the infection within three to six days after the onset of 
the symptoms. The initial symptoms are premonitory and consist 
typically of slight irritation at the site of inoculation, together with 
psychic depression. The characteristic symptoms are paralysis of 
the muscles of deglutition — which leads to extreme difficulty in 
swallowing— hyperesthesia, extreme restlessness and irritability, and 
violent reflex spasms. Even so slight an efl'ort as that required to 
swallow water frequently causes such violent paroxysms that the 
mere sight of water is distressing— hence the name hydrophobia— the 
dread of water. It is important to remember that the hydrophobic 
phenomena are much less commonly seen in rabid dogs than in man; 
' Jour. Infcc. Dis., 1918, 22, 462. = Ibid., 1919, 24, 7G. 
•> Jour. Am. Med. Assn., 1926, 86, 9.32. 
^ Hektoen: Jour. Am. Med. Assn., 1919, 72, 177. 
^ Compt. rend. Acad. Sci., 1881, 92, 159. 
