212 PHYSIOLOGICAL EEGULATIONS 



zation of water. Any ratio between a changing fraction and a 

 more fixed fraction, is suitable, and is a type of the general class 

 AE. Thus, instead of total solids (D), the content of chloride (CI) 

 or of nitrogen (N) or of protein (Pr) may be substituted. The non- 

 protein fraction need not be ascertained as such, since it is always 

 equal to (F - Pr). Hence, if Pr is the per cent of protein by weight, 



AE = A/Pr = 100 - Pr. /100^_ 100^) /lOO^ ^ ^^ /Pr, _ ,\ 



V Pri Pro // Pro \Pri / 



A non-chemical measure may equally serve, such as excess specific 

 gravity over that of water, excess refractive index, or increment in 

 depth of color. Then refractometer reading of tissue minus re- 

 f ractometer reading of water = RI, a measure of the concentration 

 of non-aqueous constituents, and 



From the data of table 23, it is concluded that in water deficit 

 diverse tissues lose water to different extents. While the whole 

 body loses 18 to 20 per cent, the skin, hypophysis, and sometimes 

 muscles, lose more. Most other tissues lose less. The four investi- 

 gations of tissue dilutions of dry substance (A/D) that are com- 

 pared, do not show close quantitative agreement. In one investi- 

 gation (columns 6 to 10) five measurements of dilution were made 

 upon each tissue sanaple. These also show little agreement, indi- 

 cating that electrolytes as well as water are redistributed. In each 

 of the latter tests, 4 to 13 days elapsed in water privation ; the body 

 weights were not reported in detail, leaving no adequate criterion 

 of body load of water. 



Also in water excess, produced in morphinized dogs by infusion 

 of 0.10 M solution of sodium chloride by vein, both relative and 

 absolute increments of water were studied in various tissues 

 (Engels, '04) (see table 29, column 2, § 91). The tissues modified 

 more than the average for the whole body are the same as those 

 modified in water deficits. 



Often it is supposed that some tissues act as depots, from which 

 water is mobilized in deficits, to which water is brought in excesses 

 (Magnus, '00). How shall a depot be defined? Evidently it has 

 to do with storage of water. Shall I look for a tank (as the camel 

 is said to have), that fills up whenever water content of the body 

 exceeds a certain value and that empties at some lower values 

 (lines MM' or NN' in fig. 115) ? If I do, I find none in the dog. Or, 



