72 SMALL-roX IN SUKKP. 



very low. Girard states, that its incubation rarely ex- 

 ceeds six or eight days dining the heat of summer. In 

 our own experiments, the period has varied consider- 

 ably : we have witnessed the appearance of the erup- 

 tion on the seventh day succeeding inoculation, and 

 we have known it to be delayed to the thirteenth day, 

 although the experiments were being carried on simul- 

 taneously : in natural cases also, the time has ranged 

 from the ninth to the twelfth day. The disease is 

 generally found to be less destructive in cold than 

 in warm and humid weather, and to produce a less 

 amount of mischief among young animals than among 

 old. 



We have no practical deductions to record with 

 reference to the progress of ovine variola when other 

 febrile and eruptive maladies exist at the same time 

 in the system; but as the lower animals cannot be 

 said to offer an exception to the rules regulating the 

 development and course of this disorder in man, we 

 shall insert the observations of Mr. Marson, whose ex- 

 perience and judgment in these exanthematous affec- 

 tions rank very high. This gentleman says — 



"It is rare to see two active diseases, such as small-pox and scarlet 

 fever, affecting the body at the same time ; as, indeed, it must be, 

 to induce a man of Mr. Hunter's great experience and obsei"vation to 

 believe that it never occurred, and to go so far as to state that no 

 two diseases of this kind could go on in the body concurrently. 

 These are his words : — ' As I reckon every operation in the body an 

 action, whether universal or partial, it appears to me beyond a doubt 

 that no two actions can take place in the same constitution, nor in 

 the same part, at one and the same time ; the operations of the body 

 are similar, in this respect, to actions or motions in common matter. 

 It naturally results from this principle, that no two different fevers 

 can exist in the same constitution, nor two local diseases in the same 

 part, at the same time.' Again : — ' In two eruptive diseases, where 



