84 FOURTH REPORT — 1834. 



The plague, according to Dr. Russell, lies dormant about ten 

 days. Among those inhabitants of Aleppo, who shut themselves 

 up after having been previously in the way of being infected, no 

 instance occurred of the appearance of the malady after the ninth 

 or tenth day. 



In a number of cases of synallpox registered by Dr. Haygarth, 

 the eruptive fever began on some day between the sixth and 

 fourteenth after inoculation. Infection by emanations was not 

 apparent until about two days later*. The latent period of 

 chickenpox is, on an average, nine or ten daysf. The pustule 

 of cowpux is distinguishable about the third day after vaccina- 

 tion, and is perfected about the tenthj. 



The contagion of measles lies dormant for ten or fourteen 

 days§. In scarlatina the interval does not exceed from two to 

 six days II . No attempts to inoculate either of those diseases 

 have yet succeeded^. 



Typhus makes its approaches in so gradual a manner, that it 

 is scarcely possible to mark distinctly its latent period. The ob- 

 servations of Dr. Haygarth indicate great latitude as to the time 

 during which typhus infection may remain dormant in the sy- 

 stem, viz. from less than ten days to even three or four weeks **. 

 The peculiar difficulty, however, of ascertaining the interval, 

 reduces greatly the value of the testimony of that careful ob- 

 server in this instance. 



Asiatic cholera in Pioissia, according to Dr. Becker, indicated 

 a latent period of from four to six days. Observations in this 

 country tend to establish a similar interval. Among all the ves- 

 sels that performed quarantine at Standgate Creek, not one ex- 

 hibited an original case of cholera after the seventh dayff. 



XXXII. When a number of persons are exposed, apparently 

 under precisely the same circumstances, to a contagious poison, 

 it seldom happens that all are affected by it. It is to individual 

 peculiarities influencing the state of the body at the time, that 

 we are to look for the causes of these varieties. The circum- 

 stances promoting the action of contagion have been classed to- 

 gether under the name of predisposing causes, which agree 

 generally in lowering the strength of the body, or depressing 

 the energy of the mind. Among these maybe reckoned fatigue, 

 want of sleep, extreme cold or heat, crowded or close places, 

 air tainted by putrefying substances, scanty or bad food, or oc- 



• Inquiry. f Heberden, Comment, cap. 96. % Jenner. 



§ Heberden, cap. 63. |j Blackburn, p. 34 



i[ The experiments of Dr. Francis Home on the inoculation of measles, have 

 not, I believe, succeeded in other hands. 



•• Haygarth's Letter to Dr. Percival. ft Cholera Gazette, No. 3. 



