930 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



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

 Gland-cells probably die within a few minutes. As to the chemical changes 

 undergone by the protoplasm in the process of dying, little can be said. The 

 composition of dead protoplasm is comparatively well known, that of living 

 protoplasm is at present 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. 1 According to Weis- 

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

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

 day, with a continuance of the proper nutritive conditions protoplasm does not 

 grow old and die ; the single individual divides into two and life continues 

 unceasing, unless accident or other untoward event interferes. With the 

 progress of evolution, however, the cells of the individual body have become 

 differentiated into germ-cells and somatic cells, the former subserving the 

 reproduction of the species, the latter all the other bodily functions. Germ- 

 cells are passed on from parent to offspring ; they never die, they are immor- 

 tal. Somatic cells, on the other hand, grow old, and at last perish. Death 

 was, therefore, in the beginning, not a necessary adjunct to life ; it is not inhe- 

 rent in primitive protoplasm, but has been acquired along with the differen- 

 tiation of protoplasm into germ-plasm and somatoplasm, and the introduction 

 of a sexual method of reproduction. It has been acquired because it is to the 

 advantage of the species to possess it ; in the simplest cases it should occur at 

 the close of the reproductive period, and in fact it frequently does occur then. 

 A superabundance of aged individuals, after they have ceased to be reproduc- 

 tive, would be detrimental to the race ; it is to the advantage of the species that 

 they be put out of the way. Death of the individual in order that the species 

 may survive has, therefore, become an established principle of nature. The 

 higher animals are better able to protect themselves from destruction than the 

 lower, and, moreover, they are needed to rear the young ; hence the duration 

 of life is frequently prolonged beyond the reproductive period. 



Weismann's theory has been the cause of much discussion, and the pros 

 and cons have been set forth by eminent biological authorities. In its appli- 

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



