3<D INANITION AND MALNUTRITION 



daphnids and aphids. How this influence becomes effective, however, is still 

 a matter of uncertainty. In view of the conclusion by some investigators that 

 temperature, rather than nutrition, is the decisive factor in sex-determination, 

 we may recall the dictum of Cuenot ('94) that "la plupart des influences de 

 milieu se ramenent en somme a des differences de nutrition." The whole 

 question requires further investigation, especially in the light of the recent 

 theory of sex-determination by the accessory chromosome. 



Effects on Cell Structure. — We have noted that the effect of inanition is to 

 produce a variable decrease in the size of the body as a whole, which is found to 

 involve a variable reduction in the various parts, organs and tissues. This, of 

 course, depends ultimately upon the changes in the underlying units, the com- 

 ponent cells of the organism. Some cells are destroyed and absorbed, others 

 persist more or less changed. From his study of the histological changes in 

 Hydra and planarians during the involution process of inanition, Schultz 

 inclined to attribute the marked decrease in size of the body to a decrease in 

 the number of cells, those persisting being practically unchanged in size. The 

 preponderance of evidence is against this view, however. Especially in the 

 adult organism, all the cells of the body during inanition tend to undergo more or 

 less atrophy. The extent and character of this atrophy vary in the different 

 tissues, and in different cells of the same tissue. The decrease in the size of the 

 body is therefore due partly to the complete disappearance of cells and partly 

 to an atrophy of those persisting. 



During the process of atrophy, the cytoplasm of the starving cells undergoes 

 in general a series of characteristic changes, first losing its stored food material, 

 pigment, mitochondria, and various inclusions. Later the cytoplasm of the 

 cells often fuses into a syncytium. Vacuolation usually appears, with progres- 

 sive decrease in amount of the cytoplasm, and terminal disintegration and com- 

 plete absorption in the case of some of the cells. There is usually an earlier 

 stage of reduction in size (simple atrophy) and a later stage of degeneration. 



The nucleus is usually more resistant than the cytoplasm, giving a higher 

 nucleus-plasma ratio. At first the nucleus may even enlarge, but later it tends 

 to shrink (pycnosis) with perhaps ultimate fragmentation, karyolysis, and final 

 absorption. The reduction in cytoplasm and relative increase in nuclear size 

 frequently gives the atrophic tissue an embryonal appearance. 



Some further special features in the atrophic cell changes may be reviewed 

 briefly. As noted by Terroine ('20) from the chemical viewpoint, the fat changes 

 show great variation among species and individuals. While fat in general is 

 quickly absorbed during inanition, in the vitelline gland cells of planarians it is 

 tenaciously retained, disappearing only when the cells undergeo final necrosis. 

 In planarians and molluscs, the nerve cells may show certain degenerative 

 changes, although the nervous tissue as a whole is remarkably resistant. It 

 may be noted that apparently the final absorption of the degenerated cells in 

 the various tissues is usually accomplished by simple solution in the interstitial 

 tissue fluids; although phagocytosis has been noted in sponges, sea-urchin larvae, 

 and especially in the case of the nemertin worm Linens. The process of phag- 

 ocytosis is said to occur also in the metamorphosis of insects. 



