692 INFECTIOUS DISEASES. 



the mucous membranes are pale and discoloured, and the skin is 

 tight and adherent to the subjacent tissues. 



These general signs, however, would not warrant a diagnosis, for, 

 apart from the cough, certain other diseases present all the external 

 appearances of the last period of tuberculosis (chronic diarrhoea, 

 chronic forms of poisoning — bacterial or otherwise — dyspepsia, etc.). 



In cases of doubt it is essential to discover by percussion and 

 auscultation that the external signs are really the result of lesions 

 of the lung, and that the lung disease has developed gradual!}^ in 

 accordance witli the signs shown b}' simple external inspection. 



The symptoms presented during the development of the pulmonary 

 lesions may be divided into three phases. 



In the first phase percussion gives no information, though auscul- 

 tation reveals rough respiration, inspiration and expiration being 

 also unequal. Expiration, which, in the healthy subject, is silent, 

 becomes clearly perceptible, not over the whole lung, but usually over 

 the anterior lobes, particularly the cardiac lobes. This sign is the 

 result of tuberculous infiltration and of the neighbouring pulmonary 

 tissue having lost its elasticity. 



Inspiration is rough and rasping, and sometimes occurs in several 

 stages, the act being interrupted or jerky ; expiration lasts longer 

 than inspiration, is rough and prolonged, but never blowing in 

 character. These peculiarities are only found in one other condition 

 of the lung, viz., emphysema. 



The patients appear little affected in this, the first, stage of tuber- 

 culosis. But for the cough they may seem perfectly healthy. 



In the second phase the tuberculous infiltration extends and ends 

 in the massing, by fusion or centrifugal growth, of the tuberculous 

 masses. 



Percussion may now indicate localised dulness, but this is not 

 invariable, because the diseased anterior and middle lobes of the 

 lung are concealed beneath the muscles of the shoulder. When 

 dulness is noted, it is usually over the lower part of the posterior 

 lobes, very rarely at any higher point on the side of the chest. 

 Frequently the dulness is only partial. 



On auscultation the signs met with during the first stage become 

 much more marked. Inspiration is always rough, rasping, painful 

 and difficult at certain points, particular!}' in the anterior zones. 

 In this region expiration is rough, prolonged and sometimes of a 

 clearly marked blowing character. This is particularly the case in 

 the sub-scapular zone and the auscultation zones 2 and 3 (Fig. 166). 

 In the dorsal region and in zone No. 1, respiration may appear 

 normal. Nevertheless, the sounds are propagated to a distance, the 



