( 37t ) 



Van Hoogènhuyze and Ykhplokgii have also examined tlie nrinc 

 of some sucklings. Always creatini]! ooidd be shown, more distinctly 

 with the reaction of Jaffé than with that of Wkyl. On account of 

 the small concentration and the trilling quantities of urine which 

 could be collected an accurate colorimetric determination was not 

 possible. In four cases however a sufficient ciuantity of urine 

 (15 — 60 cc.) was obtained, to admit at least of a somewhat reliable 

 determination. In 10 cc. urine which was diluted to 50 cc. after 

 having been mixed with picric acid and caustic soda, there was 

 found : 



I child 8 days old, 1.11 mgr. creatinine 



11 ,, ö2 ,, ,, o.yi ,, „ 



III „ 2 months „ 0.41 „ 



IV 2 17 



It is remarkable that in case III which concerned a weak child 

 which was fed exclusively on cowmilk, the quantity of creatinin was 

 so much smaller than in the three other children who were all 

 strong and brought up by human-milk. 



The above mentioned proves, as it appears to me, that the method 

 of FoLiN is an acquisition of importance of which may be expected 

 that it will aid in penetrating deeper than before into the knowledge 

 of metabolism. 



Physics. — "On the theory of reflection of light by imper/ectlij 

 transparent bodies." By Prof. R. Sissingft. (Communicated by 

 Prof. H. A. LoRENTZ). 



1. The laws of metallic reflection have been derived first by 

 Cauchy^), later by Ketteler') and Voigt '), while Lorentz') has 

 developed them from the electromagnetic theory of light. By different 



1) Cauchv, Cornpt. Rend. 2, 427, 1836; 8, 553, 6.58, 1839; 9, 7^26, 1839; 26, 

 86, 1848; Journ. de Liouv, (1), 7, 33S, 1839. Gauchy gives only general remarks 

 on the way followed by him. Derivations of the results have been given, inter 

 alia by Bekr, Pogg. Ann. 92, 402, 1854; Ettingshausen, Sitzungs-Ber. Akad. 

 Wien, 4, 369, 1855; EisENLonn, Pogg. Ann., 104, 368, 1858; Lundquist, Pogg. 

 Ann., 152, 398, 1874. 



8) Pogg. Ann., 160, 466, 1877; Wied. Ann., 1, 225. 1877; 3, 95, 1878; 22, 

 204, 1884. Ketteler has, also in consequence of Voigt's observations, modified 

 his developments, and given a final form to them in the "Theoretisctie Optik", 1885. 



3) Wied. Ann., 23, 104, 554, 1884; 31, 233, 1887; 43, 410, 1891. 



*) On the theory of refiection and refraction of light, 1875 ; Schlömilgh's Zeitschr, 

 f. Math. u. Physik, 23, 196, 1878. 



