218 OF THE BLOOD. 



planation in the same principle. 1 Thus, then, we may affirm with strong con- 

 fidence, that the liability to zymotic disease depends upon the previous condition 

 of the blood ; and more especially on the presence of fermentable matters result- 

 ing from the ordinary processes of disintegration, which, in the state of perfect 

 health, are eliminated as fast as they are formed, but of which an accumulation 

 is prone to take place, either when there are special sources of an augmented 

 production, or when the excretory operations are imperfectly performed. And 

 it would further appear, that the continued accumulation of such matters 

 may itself become a source of certain forms of Zymotic disease, which may 

 thus originate de novo in the system, and which may thence be propagated to 

 other individuals in some of the modes already specified; of this we have 

 notable examples in hydrophobia, erysipelas, and the " pustule maligne." 



211. It is not only, however, in the class of Zymotic diseases, that we seem 

 distinctly able to trace the operation of morbid poisons circulating in the blood ; 

 for there are numerous other maladies, of whose origin in a like condition there 

 can be no reasonable doubt; and these are in some respects more closely analo- 

 gous than the preceding to the disordered states induced by the introduction of 

 toxic agents. For in those of which we have now to speak, the action is desti- 

 tute of any analogy to fermentation, and its potency is strictly proportionate, in 

 each case, to the amount of the dose that is in operation. Here, too, we have 

 a connecting link afforded by those disordered states of the system, which 

 depend upon an undue accumulation of poisons normally generated within it, 

 in consequence of some obstacle to their elimination. Thus, the train of symp- 

 toms which is consequent upon the retention of urea in the blood, so much 

 resembles that occasioned by the ingestion of opium, as to have actually been 

 mistaken for it; and is as true an instance of " poisoning," as if urea had been 

 injected into the bloodvessels. So, in the asphyxia, which is produced by any 

 obstruction to the extrication of carbonic acid through the lungs, the subject of 

 it is as much " poisoned," as if he had inhaled carbonic acid from without. 

 Again, the retention of the uric acid, biliary matter, lactic acid, and other sub- 

 stances which are normal products of the waste or disintegration of the body, is 

 capable of becoming a source of morbid action in the system generally ; and the 

 evil is of course increased, when (as frequently happens) augmented production 

 is concurrent with imperfect elimination. But perversions of the ordinary dis- 

 integrating processes are also far from being uncommon, whereby, instead of the 

 substances already referred to, other products are engendered, whose presence in 

 the circulating current gives rise to trains of symptoms altogether different. Of 

 this class we seem to have an example in gout and rheumatism; the materies 

 morbi of which diseases, though probably not identical with lithic and lactic 

 acids, would seem to be formed from the decomposing matters which might nor- 

 mally have generated them. There can be no doubt, again, that many chronic 

 diseases of nutrition are attributable to a similar cause ; this being indicated by 

 the symmetrical mode in which they affect the particular parts whose condition 

 is altered ( 201). 



212. In all cases, therefore, one of the first questions which the intelligent 

 Practitioner will feel called upon to decide, is, whether the malady he has to 

 treat have its origin in the blood, or in a disorder purely local; and, if he feel 

 justified in referring it to the blood, whether it merely depend upon an alter- 

 ation in the proportion of its normal constituents, as in plethora and simple 

 anaemia, or whether its phenomena imply the presence of some toxic substance 



1 It is well known to Indian Medical Officers, that the liability to Fever, Dysentery, 

 Cholera, &c., is very much increased during, and for some time after, a severe march. For 

 a very striking example of the influence of this condition, concurrently with overcrowding, 

 in producing a terrible augmentation in the fatality of Cholera, see "Brit, and For. Med. 

 Chir. Rev." vol. ii. pp. 80-90. 



