THE HUMAN ORGANISM 



287 



although the amount of vitamin in the milk of a mother or 

 of a cow depends upon the diet of the milk-producer. It has 

 also been found that cod-liver oil is useful in many cases, be- 

 cause it contains a relatively large amount of vitamin A/ But 

 here again a great deal depends upon how the cod-liver oil 

 is prepared, for experiments show that some brands are very 

 effective, w^hile others are almost worthless (see Fig. 142). 



Posture may have a direct 

 bearing upon the vital organs: 

 cramping positions interfere with 

 breathing, with the action of the 

 stomach, with the bowels, and, 

 less directly, with the heart, 

 since they may influence the ac- 

 tivity of the larger muscles, and 

 so the circulation of the blood 

 (see Fig. 143). Good posture is 

 thus important, not only for the 

 sake of appearance but for the, 

 sake of comfort and efficiency. 



When a bone is broken, new 

 bone cells begin to form from 

 the periosteum, and the space is 



gradually filled in with solid bone. It is therefore important 

 that the broken ends (i) be set together accurately and (2) be 

 kept in position until the new formation is strong enough to 

 bear the strains of ordinary activity. In cases of dislocation 

 early replacement is necessary. Caution must be taken against 

 (i) movements that may bruise or tear muscles, tendons, or 



1 Experiments on guinea pigs and white rats, as well as observation on 

 young babies, tend to show that the effect of the vitamin A is in many ways 

 identical with the effects of exposure to sunlight. It would seem that the ultra- 

 violet rays (those portions of the sunlight that appear beyond the violet rays 

 in a spectrum) have an important bearing upon the way protoplasm works 

 over lime and that the presence of vitamin A produces similar results. Accord- 

 ing to some of the experiments it may even be that the ultra-violet rays are 

 somehow "stored" in food and later made active in the body. 



Fig. 141. Incomplete skull of 

 infant 



At several points there are rather ex- 

 tensive spaces covered only by skin 

 and connective tissue. As the bones 

 grow at and toward their edges these 

 spaces are gradually filled out 



