364 Dr. W. Henry On the Disinfecting Powers of increased 



temperature belcnv that of boiling water, appeared to me not 

 improbable, from the evidence of a fact recorded by various 

 writers ; viz. that the plague, in countries where it prevails, 

 ceases as soon as the weather becomes very hot. " Extreme 

 heat," says Dr. Russell in his Natural History of Aleppo, 

 (vol. ii. p. 339.) " seems to check the progress of the distemper ; 

 for though the contagion and the mortality increased during 

 the first heats in the beginning of the summer, a few days con- 

 tinuance of the hot weather diminished the number of new in- 

 fections. July is a hotter month than June; and the season, 

 wherein the plague always ceases at Aleppo, is that in which 

 the heats are most excessive." In another part (p* 284.) of the 

 same volume, Dr. Russell states the greatest heat at Aleppo 

 in June to have been 96° of Fahrenheit, and that of July 101°, 

 in the shade. 



Arguments, also, derived from chemical reasoning, appeared 

 to me to strengthen the probability that a temperature, raised 

 to no great extent, would suffice for the decomposition of in- 

 fectious or contagious matter*. Of the nature of contagion we 

 are, it is true, entirely ignorant. But we are entitled to conclude 

 that it is in no case identical with any one of the simple or 

 compound gases, with which chemistry has made us acquainted, 

 and which are unchanged by a temperature below 212°; be- 

 cause each of those gases has been breathed, many of them 

 very frequently, without exciting a specific disease. The sub- 

 tile poisons which propagate contagious distempers, being the 

 products of organic life and of morbid conditions of the animal 

 body, are, it is probable, of a complex nature, and owe their 

 existence to affinities which are nicely balanced and easily 

 disturbed ; even more easily than those maintaining some of 

 the products of vegetable life, which lose their original pro- 

 perties, and acquire new ones, when exposed to temperatures 

 of no great amount. Thus starch is converted by a moderate 

 heat into a substance somewhat resembling gum; and, by 

 weak chemical agents, into sugar. Among inorganic com- 

 pounds, we have a remarkable instance of the effects of heat 

 (raised however to a higher degree) in the change of phosphoric 

 into pyro-phosphoric acid. In most cases of this kind, it is pro- 

 matter existing in absorbent substances, such as wool, clothing, &c. ■ In 

 this state of confinement it seems to acquire increased virulence and 

 activity. 



* I use the term ' infection' and ' contagion' as synonymous, because no 

 sufficient distinction has been established between them. It would be un- 

 seasonable to enter, in this place, into a disquisition about words ; but those 

 who take an interest in the verbal part of the subject, will find an excel- 

 lent view of it (pointed out to mc by my son Dr. Charles Henry) in the 

 Dictionnaire dc Mcdecinc, art. Contagion, vol. v. p. 549. Paris 18 22. 



bable 



