PROLIFERATION AND REGENERATION 279 



eggs synthesize great quantities of nucleoprotein,^* even when in a 

 solution free from phospliatcs, and hero tlic only available sourc(! for 

 the phosphoric acid of the nucleins would seem to be the phospholipins 

 of the egg (J. Locb). The nucleoproteins during karyokinesis undergo 

 a chemical change in that they become of a more acid type (presum- 

 ably through splitting off of part of the proteins from the nucleic 

 acid), which results in the characteristic increase in afh.nity for basic 

 dyes, and the increased negative charge which is easily demonstrated." 

 This suggests the participation of an enzyme in the process of karyo- 

 kinesis, just as there seems to be in the production of pycnosis in de- 

 generating cells, but there seems to be no conclusive evidence on this 

 point. Gies^^ could find no enzyme in spermatozoa that incites cell 

 division in the ova of sea-urchins (Arbacia). The fertilization of 

 eggs makes them more permeable to ions," wliich possibly determines 

 many of the subsequent changes. 



In metaplasia we have what may be interpreted as a chemical alter- 

 ation due to mechanical stimuli, e. g., the formation of keratin by cells 

 that ordinarily do not do so; the deposition of calcium salts and oste- 

 oid transformation of connective tissues in rider's bone, etc. That 

 such is the case, however, cannot be positively stated from the evidence 

 at hand. 



CHEMICAL BASIS OF GROWTH AND REPAIR=8 



We do not know just what substances are necessary to maintain 

 individual cells in normal condition, what are needed to stimulate 

 them to multiplication, or what elements they require to permit them 

 to multiply, but it has been learned that certain definite materials are 

 required by the organism as a whole. It is not sufficient that a given 

 number of calories with a certain quantity of proteins, carbohy- 

 drates, fats and salts be supplied; it is essential that certain specific 

 constituents be provided among these foodstuffs. This fact was first 

 clearly pointed out by Gowland Hopkins in 1906, although in 1897 

 Eijkman had discovered that beriberi and experimental neuritis 

 might result from a one-sided diet of polished rice, and in 1902 Roh- 

 mann reported that purified food stuffs do not suffice to maintain and 

 rear mice. 



The proteins must not only provide a sufficient amount of nitrogen, 

 but they must also provide certain specific amino-acids, as has been 

 especially demonstrated by the investigations of Willcock and Hop- 



^* Not accepted by Masing, Zeit. physiol. Chem., 1910 (67), 161. 



"See Gallardo, Arch. Entwickl. Organ., 1909 (28), 125; Pentimalli, ibid., 

 1912 (34), 444. 



26Amer. Jour. Phvsiol., 1901 (6), 54. 



" See AlcClendoii, Carnegie Inst. Publ., 1914. No. 183. 



^^ See Mendel, "Nutrition and Growth," Harvey Society Lectures, 1914-15; 

 Amer. Jour. Med. Sci., 1917 (153), 1; Lusk, "Science of Nutrition," Saunders, 

 Phila., 1917. 



