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DIFFUSIBLE PHOSPHORUS UF COW’S MILK. 255 
“‘insoluble’’ salt may be dissolved up if the concentrations 
of the ions with which it is in equilibrium be diminished. 
Hence, when a quantity of milk is dialysed against a 
large volume of water the substances obtained in the 
dialysate will include not only those substances which 
exist in a state of true solution or in a dialysable or 
diffusible condition in the unchanged milk, but also those 
substances in suspension which can be made to go into 
solution by diluting with water. How considerable the 
amount of these substances may be has already been shown 
by the present author (loc. cit.). The amounts of the sub- 
stances in milk which are dialysable under these conditions 
therefore give no idea as to the amounts of dialysable or 
diffusible substances in the unchanged milk, the substance 
secreted by the mammary gland. 
In this paper, those portions of the substances present 
in milk which can be made to dialyse into a large (unlimited) 
volume of water will be distinguished as the dialysable 
substances. Those substances which exist in unchanged 
milk in a dialysable or diffusible condition will be called 
the diffusible substances. 
To determine the amount of the diffusible substances of 
milk some means are required by which these may first be 
separated without disturbing the equilibriaexisting between 
them and the remaining constituents; the process of dialysis 
as ordinarily carried out gives nohelp. A distinct advance 
in the study of diffusible substances was made by Moore 
and Bigland (1911) when they employed the method of 
dialysis against known volumes of water. - In this way the 
equilibria were displaced to a definite, although still un- 
known, extent. Another improvement in the study of 
diffusible substances was that introduced by Zuntz and 
Loewy (1894), and later employed by Rona and Michaelis 
(1909). In this method, which is known as the method of 
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