cxxx THE BEGINNINGS OF LIFE. 



upon the blood and system generally, may therefore be com- 

 pared with those unknown poisons of the zymotic diseases. 

 The great difference is this. The changes in the blood 

 induced by snake-poison are not such as to terminate in the 

 elaboration of a similar poison in any part of the body of the 

 person bitten, whilst the bite of a mad dog does lead to 

 changes which culminate in the reproduction of the hydro- 

 phobic poison ; and similarly with those of scarlet-fever or 

 small-pox — contact with these poisons entails changes which 

 result in an enormous production of similar poisons. There 

 is probably no fundamental difference between the two sets 

 of cases. The malarial miasm of intermittent fever, and the 

 poisonous state of the blood which leads to the production 

 of rheumatic fever', as a rule produce effects which are more 

 strictly comparable with those of snake-poison, though there 

 is reason to believe that these diseases may merge into other 

 affections which are admitted to be contagious — as when 

 intermittent or remittent fevers develop in warm climates 

 under the aggravated form of contagious yellow fever. In 

 this way may the gulf be bridged which seems to separate 

 the effects of snake-bite from those of hydrophobia. As 

 Liebig pointed out, what occurs in the former case may be 

 compared to the action of yeast upon a simple solution of 

 sugar, and in the latter to the action of the same ferment 

 upon a solution of sugar which also contains nitrogenous 



chloride (see 'Philosoph. Transact.' 1866, p. 5S3). Effects somewhat 

 similar, though not so lasting, are produced upon some persons by the 

 smell of powdered ipecacuanha. 



^ I agree with Dr. Richardson in thinking that this affection really 

 belongs to the zymotic class of diseases. Dengue seems to be a slightly 

 contagious affection somewhat intermediate between rheumatic and 

 scarlet fever. The ' sweating sickness ' of the middle ages was con- 

 sidered to be an aggravated epidemic form of rheumatic fever, and 

 so also with the various forms of ' miliary fever.' The contagiousness 

 of these diseases, according to Hecker, seemed to vary in different 

 epidemics. 



