118 CHEMICAL COMPOSITION OF ANIMAL TISSUES. 



not prevented even by extreme cold ; for if blood be frozen immediately 

 that it is drawn, it will coagulate on being thawed, thus preserving its 

 vitality, in spite of the freezing process, like the organized structures of 

 many of the lower animals. Again, the coagulation is accelerated by 

 exposure to air ; but it is not prevented, though it is retarded, by com- 

 plete exclusion from it. Various Chemical agents retard the coagula- 

 tion, without preventing it ; this is the case especially with solutions of 

 the neutral salts. The coagulation is not so firm, however, or the 

 fibrillation so perfect, after the use of these ; and there can be no doubt 

 that they modify the properties of the fibrine, by acting chemically 

 upon it. 



186. After remaining in this condition for a certain length of time, 

 the Fibrine undergoes a further change, which is evidently the result of 

 decomposition ; the coagulum becomes soft, and exhibits appearances of 

 putrefaction. This takes place the more rapidly, as the first coagula- 

 tion was less complete. Thus in the imperfectly-elaborated Fibrine of 

 the Chyle, the coagulum is sometimes so incomplete, that it does not 

 separate itself from the serum, and liquefies again in half an hour. In 

 certain states of disease, the solidifying properties of the Fibrine are 

 very much impaired ; so 'that it soon liquefies and decomposes. In these 

 cases, there is scarcely any trace of the characteristic fibrous arrange- 

 ment of the particles. On the other hand, the fibrinous coagulum of 

 inflamed blood, as it is more solid, is also more persistent than that of 

 ordinary blood ; and the greatest persistency of all is seen in the fibrous 

 network formed by exudation, as in the cases just now mentioned. 



187. The coagulating power of Fibrine, in other words, its peculiar 

 vital property, may be destroyed by various causes operating within 

 the living. body; so that the blood remains fluid s after death. These 

 may be classed under three heads. In the first place, the vitality of 

 the fibrine may be destroyed by substances introduced into the blood 

 from without ; which have the power of acting in the manner offermenty 

 and which occasion an obvious chemical change in its condition. Such 

 is the case in those severe forms of Fever which are termed malignant; 

 and especially those which result from the contact of putrescent matter, 

 as Glanders, Pustule maligne, &c. Secondly, it may be impaired or 

 altogether destroyed by morbid actions originating in the system itself, 

 and depending upon irregular nutrition or imperfect excretion ; thus the 

 blood has been found fluid after death in severe cases of Scurvy and 

 Purpura, also in cases of Asphyxia (consequent upon the retention of 

 carbonic acid in the blood), and in the bodies of overdriven animals. 

 The same result may follow, Thirdly, from violent shocks or impressions, 

 which suddenly destroy the vitality of the whole system at once ; these 

 may be such as are obviously capable of producing a chemical or me- 

 chanical change, as in the case of death by Lightning or by a violent 

 Electrical discharge ; or they may act through the nervous system, in 

 a manner not yet clearly understood, as when death results from con- 

 cussion of the brain, from a blow upon the epigastrium, from violent 

 mental emotion, or from a coup de soleil. It is not to be supposed that 

 the non-coagulability of the Blood is a phenomenon by any means inva- 

 riable under the foregoing circumstances; but it has been occasionally 



