"One of the most sinister features of DDT and related chemicals is the way they are passed on from one organism to another through all the links of the s. For example, fields of are dusted with DDT; meal is later prepared from the alfalfa and fed to hens, the hens lay eggs which contain DDT. Or the hay, containing residues of 7 to 8 parts per million, may be fed to cows. The DDT will turn up in the milk in the amount of about 3 parts per million, but in butter made from this milk the concentration may run to 65 parts per million. Through such a process of transfer, what started out as a very small amount of DDT may end as a heavy concentration."