806 



PERIODIC FUNCTIONS IN MAMMALS 



periodogram. Just as we use other averages in medical research, we 

 may then compute periodograms in order to describe the average 

 period or amplitude of a given bodily rhythm. 



Thus, the important use of the periodogram consists of the quantita- 

 tive description of periodicities in terms of the sample estimates of both 

 period and amplitude. These summary constants are obtained by estab- 

 lishing certain relationships between the data on the one hand, and the 

 sines and cosines of certain trial periods chosen by ourselves on the 

 other hand. The method of obtaining Schuster periodogram estimates 

 of the period (t) and the amplitude (C) for physiologic time series 

 consisting of discrete data has been outlined elsewhere (Koehler et al, 

 1956). Tables also are available which should facilitate the com- 

 putation of certain periodograms by reducing the labor involved 

 (Koehler et al, 1956). Moreover, if periodograms become desirable 

 on a larger scale, it is expedient to obtain them with the help of elec- 

 tronic computers (Fig. 1). 



C{-t) 



Fig. 1. Periodogram on rectal temperatures obtained at 4-hr intervals 

 for several days, from an individual mouse. Peak at —24 hr is well defined, 

 describing an empirically verified period. Shorter periods described by 

 higher peaks also come to the fore. Such a detailed analysis by electronic 

 computer would require an undue amount of conventional computing. 



