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of resistance as the serum contains no substances which impede 
haemolysis. 
Moreover it may be observed that also the washed blood-corpuscles 
of an anaemic animal possess a greater capacity of resistance than 
the washed blood-corpuscles of the same animal in a normal condition. 
See Table F and Fig. 6. 
Summary. 
The colorimetrical determination of the haemolysis, (ARRHENIUS) 
caused by diluted NaCl-solutions, suggests a means to compare the 
qualities of blood-corpuscles, differing as regards their capacity of 
resistance. 
With the aid of this experimental method the following results 
were obtained. 
1. New erythrocytes resist diluted NaCl-solutions better than old ones. 
2. It must be assumed that new red blood-corpuscles are built up 
out of the old ones. 
3. After venesections the regeneration greatly surpasses the loss. 
(Rule of WeEIGERT). 
4. Washing the blood-corpuscles with a NaCl-solution of 0,9 °/, 
renders them less capable of resisting diluted NaCl-solutions. 
5. The conclusion drawn from this by several workers that this 
phenomenon is caused by the removal of unknown substances, found 
in the serum, which substances impede haemolysis, is incorrect. 
Experiments have shown that if a 4°/, glucose-solution is used 
instead of a NaCl-solution 0,9°/,, this decrease in capacity of resis- 
tance does not manifest itself. 
6. The phenomenon, mentioned sub 4, should rather be viewed 
in the light of an osmotic disturbance, the principal factor of which 
is the loss of Ca, suffered by the blood-corpuscles. Indeed the capacity 
of resistance is not modified if 0,1°/, CaCl, is added to the NaCl-solution. 
7. New erythrocytes, washed with NaCl-solution 0,9 °/,, have a 
greater capacity of resistance than old ones which have been treated 
in the same way. 
May 1912. Groningen, Physiological Laboratory. 
