VARIABLE AND CONSTANT COMPONENTS 597 



started on thyroxine when they had reached a body weight of 100 or 200 g., 

 respectively. 



According to Reed and co-workers, 288 "of all the factors, including food, 

 undernutrition, fasting, muscular activity, ovariectomy, and the adminis- 

 tration of thyroxine, which we have studied thus far, the character of the 

 diet and the thyroid hormone represent the only influences that have ap- 

 preciably altered the quality of depot fat." 



5. Variable and Constant Components of Lipids 



In 1914, Terroine 342 - 343 first clearly differentiated between the two cate- 

 gories of lipids in vertebrates ; these he called the element variable (which 

 consists of the reserve fat) and the element constant (which represents the 

 essential components of the protoplasm). These will be referred to here as 

 the variable and the constant components of fat. Since it was not possible 

 to attain complete inanition in the invertebrates, Terroine 342 could not 

 separate these two groups in the lower forms. 



The concept that two types of lipids occur in the tissues is based upon the 

 fact that animals which have died as a result of fasting still contain an ap- 

 preciable amount of fat, which appears to be fairly constant for each species. 

 When the animal is forced to use this constant component as a source of 

 calories, death results shortly. On the other hand, the quantity of the 

 variable element may have a wide range; changes in this fraction, either up 

 or down, appear to have little effect upon the well-being of the animal. The 

 theory of the individuality of the function of the variable and constant com- 

 ponents of fat is based upon intensive experiments of Mayer and Schaef- 

 f er 344-847 anc j f Terroine. 348-350 A more recent exposition is to be found in 

 a review by Terroine. 351 



The variable and constant components of fats differ chemically and 

 physiologically from each other. The variable component consists almost 



342 e. F. Terroine, CompL rend., 159, 105-108 (1914). 



343 E. F. Terroine, Contribution a la connaissance de la physiologie des substances grasses 

 et lipoidiques, Masson, Paris, 1919; Ann. sci. nat. Zool. [10], 4, 5-397 (1920). 



344 A. Mayer and G. Schaeffer, J. physiol. et path. gSn., 15, 510-524 (1913). 



345 A. Mayer and G. Schaeffer, J. physiol. et path. g6n., 15, 535-548 (1913). 



346 A. Mayer and G. Schaeffer, J. physiol. et path. gin., 15, 773-788, 984-998 (1913). 



347 A. Mayer and G. Schaeffer, J. physiol. el path, gen., 16, 1-16, 23-38 (1914). 



348 E. F. Terroine, /. physiol. et path, gin., 16, 386-397 (1914). 



349 e. F. Terroine, J. physiol. et path, gen., 16, 408-418 (1914). 



360 e. F. Terroine and H. Barthelemy, Arch, intern, phijsiol, 19, 88-102 (1922); Chem. 

 AbsL, 16, 2531 (1922); E. F. Terroine and J. Weill, J. physiol. et path, gtn., 15, 549-563 

 (1913). 



351 E. F. Terroine, Ann. Rev. Biochem., 5, 227-246 (1936). 



