II CLEAVAGE AND BLASTULATION 725 



decreased viscosity of the same proteins. Specifically, "good animalization is 

 obtained for a decrease in viscosity above 14%, and good vegetalization for an 

 increase in viscosity above 28%", from a variety of animalizing and vegetalizing 

 agents. He asserts that "fibrillar shaped proteins preside over the embryonic 

 determination", and generalizes that depolymerization of fibrillar proteins occurs 

 during determination of the ectoderm of sea urchins and of the notochord of 

 amphibia. Morphogenetic effects of change of pH which might be expected to 

 produce similar effects on proteins can be reconciled with Ranzi's conclusions 

 (Yamada, 1950; Holtfreter, 1947). Needham (1955), however, feels that Ranzi's 

 attempts to generalize are forced. Ranzi (1955) continues his analysis of lithium 

 and CNS effects, and delegates a protein-stabilizing role to lithium, but feels 

 that animalizing agents cause "the initial breakdown leading to further break- 

 downs", specifically by detaching "small fragments from the fibrillar molecules". 

 "By applying all the above data to embryonic development, we may conclude 

 that a strong breakdown of preexisting proteic structures is taking place in the 

 areas hyperdeveloped by animalizing agents and inhibited by vegetalizing agents. 

 This breakdown is necessary before new syntheses can occur." 



Raven (1952) in a review of lithium in Limnaea points out, regarding increase 

 in cytoplasmic density, that this is not due to dehydration but "must be due to a 

 change in its submicroscopic structure, e.g. by increased polymerization of 

 fibrillar macromolecules in the formation of cross connections between proto- 

 plasmic fibrils. This is in agreement with the classical observations of Riinnstrom 

 in sea urchins and the more recent investigations of Ranzi and co-workers." 



{c) Observations of protozoa 



Although "development" of protozoa may be only tangentially related to our 

 problem (Lwoff, 1950), we wish to include reference to some pertinent metabolic 

 and experimental studies. Metabolic studies have been summarized by Kidder 

 and Dewey (1951). They point out that glycine appears to be required by 

 Tetrahymena for growth, and in addition, the same amino acids that are needed 

 by the growing rat, namely, arginine, histidine, isoleucine, leucine, lysine, methio- 

 nine, phenylalanine, threonine, tryptophan and valine. Glycine cannot be 

 regarded as an essential amino acid, though in large concentrations it has a 

 stimulating effect; serine and other hydroxyamino acids, however, have a more 

 marked stimulatory effect when administered in smaller quantities. The essential 

 quality of individual am.ino acids varies with the composition of the remainder 

 of the medium : valine, for example, may be omitted if sufficient quantities of 

 glycine, cystine and serine are present; conversely, unless these are present, 

 valine is required. 



Ammonium salts may also promote growth if the amino acid content of the 

 medium is suflficiently low, and provided an accessory source of carbon is provided 

 as, e.g. dextrose. 



Dewey, Kidder and Parks (unpublished, cited in review) found an inhibition 

 of their cultures by urea (700 [j,g/ml) and by a variety of urea analogs. Recently, 

 however. Seaman (1954) observes that early in the growth of the colony urea is 

 produced, but cannot be recovered even after a short time because of its destruc- 



Lileralure p. 744 



