May 20, 1920] 



NATURE 



351 



It is easy for one writing- now to see the organic j 

 connection between Riemann's thought and the 

 step made by Einstein in passing from the special 

 principle of relativity propounded in 1905 to the 

 g-eneral theory now established. The recognition 

 of the relative nature of time measuremeht had 

 already been made in the special principle, and 

 Minkowski quickly perceived that our separate 

 concepts of space and time were thereby brought 

 into a unity. It seems now but a short step to 

 apply Riemann's analysis to this four-dimensional 

 view of the universe. 



But questions still linger; the romance of re- 

 lativity, its sweeping comprehensiveness, leave 

 us breathless. When Dr. Freundlich tells us 

 that "space is banished out of physical laws alto- 

 gether : just as aether was eliminated out of the 

 laws of electrodynamics by the special theory of 

 relativity," we must pause and ask ourselves if 

 enthusiasm is not going too far. Dr. Freundlich 

 himself finds the mainspring- of Einstein's method 

 in two fundamental postulates : (i) that of con- 

 tinuity ; (ii) that of causal relationship betw'een" 

 only such things as lie within the realm of observa- 

 tion. It was the craving for continuity that gave 

 rise to Faraday's conception of tubes of force, 

 developing gradually into the electromagnetic 

 aether. It is the instinctive faith in the second 

 postulate that leads the timid to distrust the 

 formidable array of differential equations between 

 an army of variables that represent the gravita- 

 tional field in Einstein's theory. 



No physical theory has the power to forbid the 

 mind to use the firm scaffolding of Euclidean 

 truth on which to build its own representation 

 of the universe. True, it may be that the repre- 

 sentation is not so simple as we had thought; 

 that the Euclidean element of length does not 

 correspond exactly to a measured interval in a 

 rigid body. But the work of the exponents of 

 relativity is not finished until an added clearness is 

 given by them to the picture of how natural 

 phenomena are related. The aether must not be 

 put on the scrap-heap, but must be rehabilitated. 

 Space must not be spoken of as warped, for that 

 is to leave far behind the essential nature of space 

 as a mode of apprehension. The only true con- 

 tinuum is that which the mind conceives. Matter 

 cannot be a singularity in mental space ; it can 

 only be a singularity in the picture drawn upon 

 that background. Matter is one and minds are 

 many. So many minds, so many pictures of 

 matter. The correspondences between the pictures 

 are the grounds of our intellectual intercourse, the 

 ■ nly evidence of the external world which we 

 ixjssess. 



NO. 2638, VOL. 105] 



To turn over the pages of this pamphlet is to 

 encounter many questions ; nevertheless the reader 

 will have nothing but thanks to offer to the author, 

 and especially to Mr. Brose, who, while yet a 

 prisoner in an enemy country, found solace in 

 truth that transcends racial strife, and translated 

 it for our enjoyment. E. Cunningham. 



Colloidal Therapy. 



The Use of Colloids in Health and Disease. By 

 Alfred B. Searle. With foreword by Sir 

 Malcolm Morris. (The Chadwick Library.) 

 Pp. vii-fi20. (London: Constable and Co., 

 Ltd., 1920.) Price 85. net. 



B/VSED on a lecture delivered at the request of 

 the Chadwick Trustees, this volume provides 

 in compact form an account of the principal facts 

 which are known at the present time regarding 

 matter in its colloidal form, with special reference 

 to the utilisation of colloids in the normal animal 

 organism and in the treatment of disease. 



We find a lucid account of the physical proper- 

 ties of colloidal matter and of its reactions in the 

 presence of ionising- currents, of .electrolytes, of 

 radiations, etc. There is explained in simple 

 scientific language the colloidal nature of cellular 

 protoplasm and the selective permeability of cell 

 membranes for salts and colloids. 



The importance of the relatively high content 

 of the protective colloid, lactalbumin, in human 

 milk in relation to its digestibility is emphasised, 

 and the means are stated by which cow's milk 

 may be rendered more suitable for human con- 

 sumption. In discussing- the colloidal nature of 

 the blood, reference is made to the adsorption 

 theory of the conveyance of blood gases and to 

 the phenomena of haemolysis; an isotonic saline 

 solution is, however, o'g per cent, sodium chloride. 



The modern processes for precipitating colloidal 

 matter in sewage and drinking water, and the use 

 of soap as a detergent, are also briefly reviewed. 

 The author suggests that the hygienic effect of 

 sea-air is due to the presence in it of particles 

 positively charged by the beating of the waves on 

 the shore, which particles precipitate negatively 

 charged bacterial and other colloids; and in 

 regard to the invasion of the body by micro- 

 organisms, he considers that disturbance of the 

 normal colloidal condition of the body-cells or 

 fluids by undesirable electrolytes, salts, or colloids 

 of the "opposite" sign is an aetiological factor. 



The author has devoted considerable space to 

 accounts of the preparation of colloidal sols and 

 of their use in therapeutics. In the latter respect 

 he has digested the bulk of the recent and rele- 



