456 



SCIENCE 



[N. S. Vol. LII. No. 1350 



are identical with the curves for HCl or 

 H3PO4 in Fig. 1. The explanation of this 

 fact is that at the same pH the same mass 

 of originally isoelectric gelatin is in combi- 

 nation with the same quantity of these four 

 acids and since the anions of these four acids 

 are all monovalent the curves must be iden- 

 tical. 



As far as the alkalies are concerned, we 

 notice that the citrve representing the effect of 

 the weak base NH^OH on the physical proper- 

 ties of proteins is the same as that for the 

 strong bases LiOH, NaOH, KOH when 

 plotted over pH as abscissae, while the curves 

 representing the effect of CaCOII)^ or 

 Ba(OH)„ on the same properties are consider- 

 ably lower. 



It is obvious that the valency of the ion in 

 combination with the protein has a noticeable 

 influence on the properties of the protein salt 

 formed, while the protein salts with ions of 

 the same valency have all the same properties. 

 The fact of the greatest importance is, how- 

 ever, that the influence of acids and bases on 

 the physical properties of proteins is the ex- 

 pression of the combining ratios of the acids 

 or bases with proteins so that we are able to 

 predict the value of the physical properties 

 from the combining ratios. This fact seems 

 to give a final decision in favor of a purely 

 chemical theory of these influences and 

 against the colloidal theories as based on the 

 Hofmeister or Pauli ion series. 



The behavior of the proteins therefore con- 

 tradicts the idea that the chemistry of colloids 

 differs from the chemistry of crystalloids. 



Jacques Loeb 



The Eocketeller Institute 

 FOR Medical Research, 

 New York, N. Y. 



THE AFRICAN RIFT VALLEYS 



A RECENT article^ with the above title by 

 Professor J. W. Gregory, of Glasgow, is of 

 interest from the general summary that it 



i"The African Rift Valleys," by J. "W. Gre- 

 gory, Geogr. Jour., LVI., 1920, 13-47, with 6 maps, 

 7 profiles and 8 half-tone plates, and a bilbliog- 

 raphy of 65 titles. 



presents of a remarkable group of natural 

 features, as well as from the ingenious flight 

 of geological imagination by which it explains 

 them. The term, rift valley, introduced by 

 Gregory in connection with his African stud- 

 ies of 25 years ago, designates a longitudinal 

 depression " caused by the material sinking 

 in mass, so that what is now its floor formerly 

 stood level with the highlands on each side." 

 Such valleys therefore contrast strongly with 

 " ordinary valleys, which are caused by the 

 removal piecemeal by rivers or wind of the 

 material that once filled them." The omis- 

 sion of glaciers from the last clause is doubt- 

 less prompted by Gregory's disbelief in their 

 capacity to erode. 



His article opens with a general and for the 

 most part an empirical account of the " Great 

 Rift Valley " of Africa, and of the volcanoes 

 that occur along it, with little attention to 

 the structure of the region traversed, and 

 with still less attention either to the erosion 

 that the region had suffered before the as- 

 siuned rifting or to the erosion that the en- 

 closing scarps have suffered since the rifting. 

 Apart from briefly cited opinions of various 

 authors, form alone in most cases is ap- 

 pealed to in evidence of down-faulting. As a 

 result the reader may not feel convinced that 

 all the depressions described as rift valleys 

 really belong in that class. Some of the 

 limiting scarps may be purely cliffs of erosion. 

 Indeed, the inclusion of the Red Sea, with 

 the narrow Gulfs of Suez and of Akaba at its 

 northwest end and the broad Gulf of Aden 

 to the southeast of it, as rift valleys, and the 

 drawing of several " diagonal tectonic lines " 

 along certain parts of the east African coast 

 that are supposed to have been " cut off by . . . 

 faulting" suggest so open a hospitality to the 

 occurrence of rifts and rift valleys as to make 

 the reader wonder whether they are not over- 

 worked. The first part of the article is there- 

 fore chiefly valuable as a topographic sum- 

 mary of a remarkable region. A critical dis- 

 cussion of the evidence for rifting, based on a 

 review of the many articles cited in the 

 bibliography, would make an excellent subject 

 for an advanced student in physiography. 



