492 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



simultaneous occurrence of several slight disturbances of function, such as is 

 not infrequent in aged persons, may prevent the restoration of that concordance 

 among the organs without which the individual cannot live. The most con- 

 venient and most certain sign by which somatic death maybe recognized is the 

 absence of the beat of the heart, and in nearly all cases this is the criterion 

 employed. But it should be borne in mind that the failure of the heart to 

 beat is but one of the causes, and frequently a very secondary one, the primary 

 cause being then associated with other functions. It is at present in most cases 

 quite impossible to trace the course of events by which the derangement of one 

 function leads to the ultimate cessation of individual life. 



Death of the tissues or of the living substance is neither necessarily nor 

 usually simultaneous with somatic death. Constantly throughout life the mole- 

 cules of living matter are being disintegrated, and whole cells die and are cast 

 away ; life and death are concomitants. With the cessation of the individual 

 life the nervous system dies almost immediately. With the muscular tissue it 

 is very different. The stopping of the beat of the heart is a gradual process, 

 and, as Harvey long ago pointed out, the last portion to beat, the ultimum 

 moriens, is the right auricle. For many minutes after death the heart, if 

 exposed, will be found to be excitable and to respond by single contractions to 

 single stimuli. Irritability is said to continue in the smooth muscle of the 

 stomach and the intestines for forty-five minutes, and considerably later than 

 this the striated muscles of the limbs can still be made to twitch by proper 

 stimuli, in the cat and rabbit after twelve or fourteen hours. 1 Gland-cells 

 die probably within a few minutes. As to the chemical changes undergone 

 by the protoplasm in the process of living, little can be said. The composi- 

 tion of dead protoplasm is comparatively well known, that of living proto- 

 plasm is at present largely a blank ; and, although investigation has gone suf- 

 ficiently far to offer a basis for several suggestive hypotheses, the latter are too 

 abstruse for lucid discussion in the present space. Neither in somatic death 

 nor in the death of the tissues does the body lose weight. Within fifteen or 

 twenty hours it cools to the temperature of the surrounding medium. Rigor 

 mortis, due to the coagulation of the muscle-plasma within the muscle-cells, 

 begins within a time varying with the cause of death from a half hour to 

 twenty or thirty hours, and continues upon an average twenty-four to thirty- 

 six hours. Then the tissues soften, and soon putrefactive changes begin. 



Theory of Death. — It has been intimated that all the tissues are destined 

 to die. An exception must be made in the case of those germ-cells, both male 

 and female, that are employed in the production of new individuals. They 

 pass from one individual, the parent, to another, the offspring, and thus cannot 

 be said to undergo death. This is the basis of Weismann's theory of the 

 origin and significance of death in the organic world." According to Weis- 

 mann, primitive protoplasm was not endowed with the property of death. 

 As found in the simplest individuals, like the Anxrha, even at the present 



' Lee, Adler, and Balkley : American Journal of Physiology, 1900, iii. p. xxix. 

 2 A. Weismann: Essays upon Heredity, 1889, i. 



