THE REACTION TO FOOD 339 



Doses of 0.00 1 mg. daily suffice to cause the healing of a 

 rachitic lesion in little rats. It appears, however, that other 

 substances among the sterols are capable of possessing the 

 vitamin d property. The sterols which can acquire vitamin 

 potency are activated by exposure to ultraviolet irradiations. 

 It appears that in the tropics where there is much ultra- 

 violet energy from the sun, the rays with certain frequencies 

 activate the pro-vitamin d contained in the skin. This is 

 then transported throughout the body and becomes a 

 regulating agency in bone calcification. In those parts of 

 the world where radiant energy from the sun is low, or for 

 long periods non-existent as in the polar regions, this defi- 

 ciency must be made good by the consumption of oils 

 from marine sources. In the north temperate zone where 

 the great centers of population subsist in a climate where 

 little of the skin surface can be exposed to light during the 

 colder parts of the year, and where only small quantities 

 of marine food are eaten, rickets among children and animals 

 is most prevalent. An important factor appears to be the 

 smokiness of the atmosphere of cities which tends to filter 

 out much of the radiant energy of a frequency capable of 

 activating the pro-vitamin d. It is for this reason that the 

 practice has now become established throughout the United 

 States and much of Europe of giving cod liver oil to infants 

 as a routine measure of protection against the development 

 of rickets. 



A substitute for cod liver oil is now much promoted in 

 the form of radiant energy derived from the quartz mercury 

 vapor lamp which is rich in wave lengths of frequencies 

 necessary for the activation of pro-vitamin d. While there 

 can be no doubt of the effectiveness of this physical sub- 

 stitute for the chemical principle, vitamin d, there is little 

 justification for the extraordinary enthusiasm shown by 

 many physicians and lay persons for treating all manner 

 of ailments with the ultraviolet lamp. No evidence has 

 yet been brought forward which indicates that the ultra- 

 violet lamp is effective in any other condition than in 

 safeguarding skeletal development. 



Vitamin f has much the same distribution as vitamin b, 

 but is apparently considerably more abundant in lean meat 



