304 



GENERAL PHYSIOLOGY 



plays an extremely important rdle in the animal body. Preyer 

 found the composition of hsemoglobin to be — 



Although at first this formula caused surprise, a number of later 

 analyses have since given quite similar results.^ 



Thus, according to Grlibler's investigations ('81), the compo- 

 sition of the crystallised proteid which occurs in the squash-seed 

 may be estimated as — 



^292-f-481-'^ 90^83^2- 



Zinoffsky ('85) found the formula of haemoglobin from horse's 

 blood even still larger than Preyer — 



Similarly complex formulas have been derived for the proteid 

 that constitutes the white of the hen's egg. From all these analyses 

 it follows that because of the mass of its constituent atoms the 

 proteid molecule must be enormous. 



The great size of the molecule explains an important character- 

 istic of proteids, viz., that, in contrast to other bodies, they do not 

 diffuse from solutions through animal membranes or artificial 



parchment. If an aqueous solution 

 of common salt or any other soluble 

 salt be placed in a wide glass tube, 

 the lower end of which is closed by 

 a membrane, preferably artificial 

 parchment (Fig. 37), and the tube 

 be suspended in a vessel of pure 

 water, it is found after a short time 

 that the concentration of the salt 

 solution in the inner tube has de- 

 creased considerabl}', while the water 

 in the outer vessel has come to have 

 an equal percentage quantity of salt. 

 Hence salt has diffused from the 

 tube through the membrane into 

 the outer water until its percent- 

 age composition has become equal 

 in the two liquids. But if instead of the solution of salt a solu- 

 tion of egg albumin be employed, which can be obtained by rubbing 

 up thoroughly the white of a hen's egg with about 100 cubic centi- 

 metres of water and filtering, the solution can be allowed to stand 

 in the dialyzer (as the apparatus is called) for hours and days 

 without a trace of albumin diffusing from the inner tube into the 

 outer water. This phenomenon may be explained very simply from 



1 Cf. Bunge ('94). 



Fig. 37. — Dialyzer. 



