REPR 01) UCTION. 491 



Thus with the progress of age the nuclei become small and irregular in out- 

 line, and the cytoplasm pigmented, while the nucleoli are often wanting. The 

 nuclear differences are even more marked in the cerebral ganglia of lues, where 

 moreover, aged individuals possess a smaller number of nerve-cells than the 

 young. The nuclear differences accord with the common belief thai the nucleus 

 is the formative centre of the cell. It has been shown that a decrease 

 in the weight of the whole brain occurs in both men and women, beginning in 

 the former at about fifty-five years, in the latter at about forty-live years. In 

 eminent men the decrease begins later. The thickness of the cortex and the 

 number of tangential fibres in it diminish especially after fifty years, and this 

 probably signifies a loss of cells. There is a decrease in general brain-power, 

 in power of origination, in the power to map out new paths of conduction and 

 association in the central nervous system and thus to form habits. Reaction- 

 time is lengthened. The delicacy of the sense-organs is noticeably less, and in 

 the eye the hardening of the crystalline lens and the weakening of the ciliary 

 muscle diminish the power of accommodation. The muscles atrophy and mus- 

 cular strength is reduced. The pineal gland, ligaments, tendons, cartilage, and 

 the walls of the arteries, show a tendency toward calcification, and the bones 

 become more brittle. Subcutaneous adipose tissue disappears, but a fatty de- 

 generation of cells is not uncommon, notably in all varieties of muscle-cells, 

 in nerve-cells, and probably in gland-cells. The pigment of the hairs disap- 

 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 ' 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 thai 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 "I' 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 ^vxvv<- 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 kidney- 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 

 1 F. Boas: Verhandlungen da- Berliner Anthropologischen QezeUschaft, L895. 



