The elaboration of newer methods for the determination of lipoids during the past few years has resulted in an increase in the literature on the subject; notwithstanding this added knowledge, the rôle played by these substances in the general body metabolism is neither clearly nor fully understood. One of the underlying reasons for this failure to evaluate properly the function of the lipoids is the insufficient data as to their normal incidence especially during infancy and childhood. Additional data on the normal values during these periods may be of some aid.
The collective term "lipoids" encompasses a heterogeneous mass of substances which are found after extraction of animal or vegetable tissue with ether or alcohol or a mixture of the two. Some of the substances obtained by extraction are fatty; they yield fatty acids on hydrolysis but differ from neutral fats in that they contain nitrogen or nitrogen and phosphorus;