1345 
Our choice is explained by the fact that one of us *) (when he 
was comparing the sugar-percentage of blood-serum and that of the 
ultra-filtrate of this serum), made the unexpected discovery that in 
the process of ultra-filtration a considerable portion of the substance, 
causing the reduction, remains behind. The above-mentioned differ- 
ence in the sugar-percentage between serum and its ultra-filtrate *) 
has been described at about the same time by Rusznyak *). The 
problem of combined sugar now again came to the fore. By the 
researches of v. Hess and Mc. Gurean ©), using Ager’s °), method of 
vivodiffusion, and of Mricmarris and Rona *) it seemed to have been 
solved in this sense that all the sugar in the blood occurred in a 
free state. Here we can leave out of consideration (as unsolved) the 
question whether the reducing substance which remains behind in 
ultra-filtration, is really combined sugar or whether it must be 
accounted one of the substances which give the so-called ‘rest- 
reduction”. We would only observe here that we should have to 
accept that what does not pass the ultra-filter, is really glucose, if 
we relied on the investigations of Ear’). This author found that of 
the total reduction of the blood, determined by a slightly modified 
method Bane (also used by us), only a very small part should be 
ascribed to this rest-reduction. For convenience sake we shall call 
the difference which was found, “combined sugar’. 
When the difference in sugar-percentage between the serum 
(containing colloids) and the ultra-filtrate (containing no colloids) 
had been established, this problem presented itself to us: in how 
for can those liquids of the body, containing like the ultra-filtrate 
only insignificant quantities of albumen and colloids in general (such 
as humor aqueus, cerebro-spinal fluid, amnion-liquid) be compared 
with ultra-filtrates of the blood, also as regards their chemical com- 
IS. VAN CREVELD: Communication “Physiologendag” 16 December 1920, 
Amsterdam. Report to appear in Arch. Néerl. de Physiologie. 
*) We wish to draw attention to a communication by HAMBURGER and 
BRINKMAN (Biochem. Zeitschr. 88, 103, 1918). These authors did not find a 
difference between the serum and its ultra-filtrate. But their results were 
based only on provisional investigations, the chief aim of their researches 
lying in a totally different field. Undoubtedly HAMBURGER and BRINKMAN 
would by continuing their investigations have found the difference which is 
mostly present and considerable. 
8) RuszNyak. Biochem. Zeitschr. 113, 52, 1921. . 
*) ABEL, ROWNTREE and TURNER, Journ. of Pharmac. and Exp. Ther. 5, 
275 and 611, 1914. 
5) v. Hess and Mc. Guiaan. Ibid. 6, 45, 1914. 
6) MicH4ELIS and Rona. Biochem. Zeitschr. 14, 476, 1908. 
1) Ear. Biochem. Zeitschr. 107, 229, 1920. 
87* 
