March 14, 1913] 



SCIENCE 



395 



Thus it is that the regulation of reaction 

 of blood and protoplasm manifests the very 

 highest stability.* 



In exactly the same way that neutrality 

 is favored by the ionization constant of 

 phosphoric acid, the excretion of acid is 

 facilitated. By variation of the relative 

 amounts of acid and alkaline phosphates 

 the relative amounts of acid and basic con- 

 stituents of the urine may be varied in the 

 highest degree, accompanied by the very 

 smallest possible variations of hydrogen 

 ion concentration. Thus the presence of 

 phosphoric acid makes of the urine an ideal 

 regulatory apparatus for the preservation 

 of the normal ratio of acid to base in the 

 blood. 



Such are the more striking aspects of 

 this subject. Neutrality is quite as defi- 

 nite, quite as fundamental and quite as 

 important a characteristic of the organism 

 as its temperature, or osmotic pressure, or 

 in fact anything else that we know. And 

 it turns out to possess those remarkable 

 characteristics of stability that have been 

 revealed by the researches of Rubner and 

 others in the case of temperature, only in 

 far higher degree. 



Within wide limits of amount any acid or 

 base may be poured into the organism, and 

 the reaction will not vary ; nor will it vary 

 if such be produced by the organism, and 

 this constancy will protect all enzymatic 

 processes, the fiinction of respiration and 

 the whole distribution of material through- 

 out the body. 



Let us return to Cuvier's vortex. Into 

 it let us pour anything, for example hydro- 

 chloric acid. No sooner has it entered than 

 it is neutralized, and neutralized it remains 

 until, on leaving the body, it appears as 



" For a larger survey of this whole subject two 

 articles in the Ergebnisse der Physiologie, VIII., 

 254, 1909 (the author) and XII., 393, 1912 

 (Sorensen) may be consulted. 



sodium chloride, ammonium chloride and 

 a slightly heightened excess of acid phos- 

 phate over alkaline phosphaie in the urine. 

 The urine is variable, the ingesta are 

 variable, even the products of metabolism 

 are variable; but, while life endures, the 

 dynamical equilibrium of hydrogen and 

 hydroxyl ionizations persists. 



L. J. Henderson 



Harvard TJni^'ersity 



THE FHTSIOLOGICAL SIGNIFICANCE OF 



SOME SUBSTANCES USED IN THE 



PBESEBVATION OF FOOD '^ 



Food preservatives are those substances 

 which delay or prevent the decomposition 

 of food as a result of the action of bacteria 

 or other ferment-producing organisms. 

 Other substances, sometimes classed as pre- 

 servatives, and in the popular mind asso- 

 ciated with them, are not so much pre- 

 servatives as agents for the conservation of 

 some special property of the food in ques- 

 tion, as, for example, the use of copper 

 sulphate in the fixation of the color of 

 green vegetables. A large number of 

 bodies may be included under the head of 

 preservatives, but our interest to-day cen- 

 ters in the so-called "artificial" or "chem- 

 ical" preservatives, because of the ques- 

 tion of the permissibility of using them. 

 Some of these bodies have been condemned 

 largely because of their origin, because of 

 their artificial character, which basis of 

 condemnation can not be regarded as sufii- 

 cient or scientific. 



Their merits or faults must be decided 

 on the basis of physiological behavior, es- 

 sentially, and from this point of view I 

 wish to speak of several substances con- 

 cerning which the discussions have been 



^A paper read before the Fifteenth Interna- 

 tional Congress on Hygiene and Demography, 

 Washington, September 23, 1912. 



