REPRODUCTION. 929 



pears. The size of the muscles, the liver, the spleen, the lymphatic and prob- 

 ably the digestive glands, decreases. The heart and the kidneys seem to retain 

 their adult size. The vital capacity of the lungs, the amounts of carbonic acid 

 and of urine excreted, diminish. The rate of respiration and of the heart-beat 

 rises slightly. Ovulation is wanting, and the power of producing spermatozoa 

 is lessened. The stature undergoes a slight and steady decrease. Boas 1 has 

 shown that in the North American Indian this continues from about thirty 

 years of age onward. All of these changes, the details of which should be care- 

 fully studied and reduced to anatomical and physiological exactness, demonstrate 

 that senescence is characterized by a steady diminution of vitality. 



Death. Sooner or later vitality must cease and the change that is called 

 death must come. The term " death " is used in two senses, according as it is 

 applied to the whole organism or to the individual tissues of which the organ- 

 ism is composed. The former is distinguished as somatic death, or death 

 simply, the latter as the death of the tissues. 



Somatic death occurs when one or more of the organic functions is so dis- 

 turbed that the harmonious exercise of all the functions becomes impossible. 

 Thus, if the brain receives a severe concussion, the co-ordination of the organs 

 may be interrupted ; if the respiration ceases, the necessary oxygen is withheld ; 

 if the heart fails, the distribution of oxygen and food and the collection of 

 wastes come to an end ; if the kidneys are diseased, the poisonous urea is 

 retained within the tissues. A continuation of any one of these profound 

 abnormal conditions, which may be brought about by accident or disease, or a 

 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 may be 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 



1 F. Boas : Verfiandlungen der Berliner Anthropologischen Gesellschafi, 1895. 

 59 



