Changes in the =cardio-vascular system= are among those which are not altogether understood, and it is still a moot question as to whether or not there is an actual increase in the amount of maternal blood during pregnancy. But results of the most recent investigations suggest that there is a definite increase in both the cells and the plasma. This increased amount circulating through the heart subjects it to a certain amount of strain, with the result that the organ is slightly hypertrophied and the pulse pressure is higher. The =respiratory organs= do not show any marked alterations. The upward pressure of the enlarging uterus gradually shortens the height of the thoracic cavity, but if it grows sufficiently wide in compensation, there is no decrease in the capacity of the lungs. If this does not occur, the patient may suffer from shortness of breath. The larynx is sometimes reddened and edematous, a fact which explains the damaging effects which child-bearing may have upon the voice of singers. Changes in the =digestive tract= during pregnancy are the morning sickness already described, and constipation. The latter is suffered by at least one half of all pregnant women, and is due chiefly to pressure of the uterus on the intestines, though impaired tone of the stretched abdominal muscles may be a factor. This condition is most troublesome during the latter part of pregnancy. There also may be gastric indigestion causing acidity, flatulence and heartburn, and intestinal indigestion giving rise to diarrhea and cramp-like pains. The appetite may be very capricious during the early weeks, and become almost ravenous later on. Changes in the =urinary apparatus= include frequency of micturition mentioned among the symptoms of pregnancy. The changes in the =bony structures= of the pregnant woman are characterized by partial decalcification. This is accounted for by the fact that the developing fetus requires a definite amount of calcium in the formation of its osseous structures, and unless the expectant mother absorbs an adequate quantity from her food, it must be extracted from the bones and similar structures, such as the teeth. Her bones and teeth accordingly grow softer, and we have the well-known adage, “for every child a tooth,” as well as the fact that fractures during pregnancy unite very slowly. There are also the softened cartilages which were referred to in connection with the anatomy of the pelvis. A part of the softening of the pelvic cartilages, however, is due to a temporarily increased blood supply. As will be explained in the chapter on nutrition, this partial decalcification of the mother is entirely unnecessary, and the newer knowledge of nutrition points the way to its prevention.