GRAMS 















\#3 



- 



600 

 400 



- 



p' 



/ 

 i 



d 



6 yP^ 



! ^ 



□a/ 



1 



1 



D 



4^ 



-A 



?Ca 

 \#2 



A 





- 



200 





'a 





#1. 



#2. 



a a SPE 



A— A SPE 







n 





1 



i 



#3. 



o o SP 8 



1 i 



HVO 



i 





200 400 600 800 1,000 



DAYS 



Figure 2. — Weight in relation to age of selected individual rats fed SP 8 HVO and SPE diets. 



still more rapid weight gains for animals fed a 

 synthetic diet. 



Inherent differences in the growth potential of 

 different strains of rats complicate comparison of 

 the size of animals from different laboratories. 

 Mature animals from the stock colony maintained 

 in this laboratory appear to weigh as much as or 

 more than most stock rats of comparable age from 

 other laboratories. Their average maximum 

 weight was slightly less than the 522 grams re- 

 ported for the rapid-growth-producing diet of 

 Anderson and Smith (.9). Rats fed the semipuri- 

 fied diet reached weights comparable to those 

 observed by Mayer (127) using a synthetic diet. 



Numerous equations have been suggested to 

 represent changes of weight with age, and several 



investigators (44, 58, 78) provided evidence for 

 the usefulness of the equation proposed by Zucker, 

 Hall, Young, and Zucker (194) for evaluating rat 

 growth and relative efficiency of various experi- 

 mental diets. These authors proposed an empiri- 

 cal formula for expressing growth which defines K, 

 a growth intensity factor, and A, an inherent size 

 factor. When the formula was applied to data 

 from their laboratories as well as to data from 

 other laboratories, these authors report that a 

 straight line was generally observed and that 

 neither size nor growth rate appeared to affect 

 the growth property measured by K, the slope of 

 the line, as long as the diets were free from growth- 

 inhibiting factors. Dunn, Murphy, and Rock- 

 land (53), however, observed a change in the 



GRAMS 



600 



400 



200 



74 



56 34 24 



69 / <\_~ v 13 



21 12 , 



3 ^o-O- ^. 



LONGITUDINAL DATA* 



a — a SP 8 HVO 

 o— -o SPE 



CROSS-SECTIONAL DATA** 

 — o Stock 



_j I I J_ 



200 



400 



600 



800 



DAYS 



#NUMB£R OF RATS SURVIVING; ANIMALS INCLUDED AS LONG AS HEALTHY. 

 **EACH POINT REPRESENTS DATA FOR AT LEAST IS ANIMALS. 



Figure 3. — Average weight in relation to age of rats fed stock, SP 8 HVO, and SPE diets. 



13 



