94 IMMEDIATE PRINCIPLES OF THE TISSUES. 



tonitis the acute pain accruing from motion secures rest of the dis- 

 eased part. Mucous membranes, lining canals for the passage of 

 foreign substances, are, on the other hand, unfavorably situated in 

 this respect, since the latter may disturb the contact of the exuda- 

 tion, or even remove it entirely. The latter, however, often does 

 not occur, and therefore false membranes (falsely so called 1 ) may be 

 formed on the pharynx, in the rectum, the vagina and uterus, and 

 the nasal passages ; and in the larynx, trachea, and bronchial tubes, 

 especially of young children. 



5. When a temperature of 98 to 100 Fahr. is uniformly main- 

 tained. Here an internal surface or part has the advantage. 



V. On the other hand, all the circumstances opposing the con- 

 ditions just mentioned render the fibrillation less perfect. These 

 need not be specified at length. Any agent reducing the vitality of 

 the fibrine, diminishes the probability of the formation of a false 

 membrane, in case of inflammation on a serous surface. Alkalies, 

 nitrate of potassa, and the salts of mercury (the protochloride espe- 

 cially), appear to possess this property, causing the exudation to 

 remain longer fluid, and thus prolonging the opportunities for its 

 reabsorption. Hence, if these agents are administered too freely, 

 and especially when the fibrine has already a low vitality (as in 

 scrofulous subjects), the exudation may be converted into pus in- 

 stead of a false membrane. Empyema may thus be produced from 

 pleuritis, in a delicate patient. 



VI. The coagulation of the blood may be entirely prevented by 

 any cause which at once destroys the vitality of the fibrine. Such 

 are 



1. Poisons in the blood, as in case of malignant typhus, or of 

 glanders; or of retention in the blood of deleterious secretions, as 

 carbonic acid gas (in asphyxia), urea (in suppression of urine), &c. 



2. Violent shocks to the nervous system, as from mental emotions, or 

 in cases of death from lightning. 



3. Too high a temperature. A heat of 180 destroys the vitality 

 of the fibrine, and coagulates the albumen of the blood. 



VII. The following agents retard the coagulation of the blood: 



1. Extreme cold. If blood is, however, frozen at once on being 

 drawn, it coagulates on being thawed. 



2. Certain narcotics and sedatives, as opium, belladonna, aconite, 



1 See section on "False Membranes." 



