NECROSIS AND DEATH. 265 



Thus muscular rigor appears usually in a few minutes after 

 death and is of brief duration in animals, that have died as a 

 result of a long continued exhaustive disease, as chronic tuber- 

 culosis. On the other hand rigor mortis may not become evi- 

 dent until 24 hours after death in animals that have been killed 

 while m a perfect state of health and it may continue for from 

 two to four days. In catalepsy, muscular rigidity is a charac- 

 teristic symptom. Other conditions, however are sufficient to 

 differentiate this from rigor mortis. 



Decomposition or putrefaction is caused by the action of putre- 

 fying bacteria. 



The decomposition of a tissue is sufficient evidence of the fact 

 that it is lifeless. Decomposition or putrefaction is not easily 

 detected in the early stages. The evolved odor is usually the 

 accepted sign of decomposition and during some seasons of the 

 year, decomposition may not become evident for several days 

 after death. The carcasses of animals dead of septic infections 

 usually decompose immediately after death, e. g. carcasses dead 

 of anthrax, hog cholera, etc. 



Tests. — Because of the uncertainty of the above signs espe- 

 ciall>', during the first 24 or -18 hours after death, certain tests 

 are recommended to determine the presence or absence of life 

 in a certain body. They, like the above signs, are not absolute. 



Tlic mirror test. — ^Respired air contains more or less water 

 vapor. Respiration is not always percejitible. Water vapor is 

 condensed upon a cold surface. The procedure of this test con- 

 sists in holding a mirror over the nostril and if any air is ex- 

 pired the watery \apor from the expired air will be condensed 

 and rendered visible upon the surface of a mirror. This test is 

 not infallible for the respiratory functions may be so diminished 

 that the moisture (watery vapor) of the expired air is insufficient 

 for condensation upon the mirror. 



Blister Test. — Blisters or vesicles can usually be produced by 

 heat or chemic vesicants applied to the skin of a body in which 

 life still exists. The formation of vesicles is not possible in dead 

 tissue because the production of a blister represents the response 

 of a living tissue to an irritant and only living tissues are cap- 

 able of reacting. Vesicle productions varies in living animals 

 and in some cases they are not produced. 



Incision. — Because of the elasticity of living tissues, all incised 

 wounds gap in the living body. Tissue elasticity disappears 

 when the tissue dies, consequently incised wounds in dead tis- 

 sues do not gap. 



