VARIABLE AND CONSTANT COMPONENTS 601 



phospholipid content increases to a maximum concomitantly with an in- 

 crease of activity to the highest pitch. 361-363 On the other hand, no similar 

 variation occurs in the cholesterol fraction. When the corpus luteum re- 

 lapses into inactivity, the phospholipid content decreases, while that of 

 cholesterol increases. 



A lack of uniformity in the phospholipid and cholesterol content of 

 muscles has also been demonstrated. In fact, Bloor 364 ' 365 alone and with 

 Snider 366 reported that the phospholipid and cholesterol content of muscles 

 cannot be assigned a fixed value. Differences in the quantities of these 

 components were shown to exist between voluntary, involuntary, and car- 

 diac muscle in the same animal, between different muscles of the same type, 

 according to the extent of the activity, and finally between identical mus- 

 cles in different species of animals. Both phospholipids and cholesterol 

 are higher in malignant than in benign tumors. 367,368 Sinclair, 369 in a review 

 of the physiology of phospholipids, cited a number of other instances in 

 which the concentration of phospholipids was altered by the physiologic 

 activity of the tissues. Bloor 1 believes that the constant factor in tissue 

 lipids is a valuable feature in characterizing a tissue or organ, especially in 

 species having settled habits of activity. 



In further support of the theory that lipids in the constant component 

 exhibit not only a quantitative constancy but also a qualitative constancy, 

 Terroine and Belin 352 suggest that the phospholipids are not constant in 

 composition in the static sense, but rather in the dynamic sense. The con- 

 stancy is a consequence of two types of processes operative in opposite 

 directions ; one of these tends to modify the element constant and the other, 

 which depends upon the specific properties of the tissues, attempts to re- 

 constitute it. 



However, the present balance of opinion is contrary to the concept that 

 the composition of the phospholipids is constant. In the first place, Ayl- 

 ward and co-workers 370 believe that the above hypothesis is in contradiction 

 to that of the activity of the phospholipids in fat metabolism. Moreover, 

 Sinclair has consistently denied that phospholipids are uniform in composi- 



361 W. R. Bloor, R. Okey, and G. W. Corner, /. Biol. Chem., 86, 291-306 (1930). 



362 R. Okey, W. R. Bloor, and G. W. Corner, J. Biol. Chem., 86, 307-314 (1930). 



363 C. Kaufmann and K. Raeth, Arch. Gynakol., 130, 128-151 (1927). 

 361 W. R. Bloor, /. Biol. Chem., 72, 327-343 (1927). 



368 W. R. Bloor, J. Biol. Chem., 114, 639-648 (1936). 



366 W. R. Bloor and R. H. Snider, J. Biol. Chem., 107, 459-470 (1934). 



367 M. Yasuda and W. R. Bloor, J. Clin. Invest., 11, 677-682 (1932). 



368 R. Bierich and A. Lang, Z. physiol. Chem., 216, 217-223 (1933). 



369 R. G. Sinclair, Physiol. Revs., 14, 351-403 (1934). 



370 F. X. Aylward, H. J. Channon, and H. Wilkinson, Biochem. J., 29, 169-178 (1935). 



