Organs of Respiration and Circulation. 



605 



compresses the air-cells of the lungs, and prevents the entrance 

 of the atmospheric air into them ; hence the absence, in the 

 advanced stages of pleuro-pneumonia, of the respiratory sound 

 in the affected parts. The great depth in the colour of some of 

 the patches is also produced by the same cause ; for the pigment 

 of the accumulated corpuscules cannot be decarbonized, from the 

 non-entrance of the oxygen of the air into the cells. 



I have already remarked that the vitiated atmosphere does not 

 act as a direct irritant to the pulmonary tissues or mucous mem- 

 brane of the air- passages, a fact which is proved by the absence 

 of all the usual symptoms of catarrh, laryngitis, or bronchitis, as 

 precursors of pleuro-pneumonia. Besides, if such were the case, 

 both lungs would be equally affected ; whereas it is well known 

 that the disease is very partial, and that the right lung is princi- 

 pally involved (see fig. 21). The aerial poison, whatever may be 

 its nature, being carried by the ordinary process of respiration 

 into the air-cells of the lungs, exerts its baneful influence upon the 

 blood in its circulation through the capillaries. The blood thus 

 impregnated with something detrimental to its healthy condition 

 undergoes changes similar to the solids when diseased, and these 

 changes are figured forth in the pulmonary tissues. 



Each organ of the body seems susceptible of being acted upon 

 in a special manner by deleterious matters entering the circu- 

 lation : thus the poison of small-pox reacts on the skin ; that of 

 glanders on the mucous membranes of the nasal cavities,' — of 

 rabies on the nerves, — of eczema on the lips, tongue, and feet, — 

 and of pleuro-pneumonia on the lungs. 



The amount of the deleterious matter received at each inspi- 

 ration appears to be insufficient to interrupt at once the functions 

 of the lungs, for, were this the case, death would speedily occur 

 from asphyxia. ; whereas we have constant proofs that the disease 

 we are considering is partial in its attack, and insidious in its 

 nature, making its way stealthily ; being very often unobserved, 

 until it has made great inroads on the constitution. This cha- 

 racter of the affection is alone sufficient to create a doubt of its 

 being inflammatory, for inflammation of the lungs, even at its 

 commencement, is marked by unmistakable indications of ill- 

 health. The absence of the ordinary symptoms of pneumonia, 

 together with the peculiar changes observed in the lungs, have 

 satisfied me that pleuro-pneumonia is not of an inflammatory 

 nature at its outset, and that inflammation is rather the result than 

 a cause of the disease. It is difficult to explain the precise change 

 which takes p ace in the blood from the operation of the aerial 

 poison ; but it appears to me that the vitality of the fibrine is in- 

 terfered with, and that it, with the albuminous constituents of the 

 fluid, also altered in quantity, is transuded from the capillary 



