Osmotic Eqiiilihnitloii. 231 



blood, but also the chemical composition, salt ratios, surface 

 tension, and viscosity of the blood, as well as standardisation 

 of body temperature, rate of heart beat, and rate of respira- 

 tion ; the higher the animal the greater is the degree of stan- 

 dardisation of its various functions. 



Those animals, however, which had remained in the sea, or 

 the early descendants of the primitive terrestrial animal which 

 had migrated back to this ocean which Macallum (6) places in 

 precambrian times must, since those times, have had a constant 

 fight against the increasing concentration of the ocean. On the 

 other hand, those primitive creatures which had betaken them- 

 selves to the fresh water must have had a fight against the ten- 

 dency to dilution of their body fluids. 



With what mechanisms, then, is the animal organism en- 

 dowed which enable it to oppose environmental influences 

 affecting the osmotic pressure of its blood? 



We know that one of the chief functions of the kidneys is 

 to maintain the osmotic pressure of the blood constant, and, 

 since in the mammal (for we know more of mammals and are 

 better able to study them) there is a constant drain of water 

 from the blood to supply the sweat and saliva, both very watery 

 fluids (all other secretions being more or less isotonic with 

 blood), the kidney is normally called tipon to secrete a fluid 

 whose osmotic pressure is generally very much above that of 

 the blood. In this connection the results of Sommerfeld and 

 Roder (13) are of interest. The osmotic pressure of the urine 

 of a suckling fed on dift'erent milk diets was determined, and 

 it was found that on a diet of full cow's milk the urine had a A 

 of 0. 736^0, and on iis mother's milk the urine of the suckling 

 gave a A of 0.746^0. But there is another means at the disposal 

 of the organism, and that is by allowing entry into the alimen- 

 tary canal of foods whose osmotic pressure is not above that of 

 the blood, or in the case of sea animals (teleosts upwards), where 

 this is not possible, either the non-absorption of the extra saline 

 constituents of the sea-water, or if the absorption of these sub- 

 stances does take place, their elimination by the kidney. Bot- 

 tazzi (1) has shown in the case of the marine teleosts that the 

 latter process takes place, but whether marine mammals have 

 adopted this practice, or whether they simply do not absorb 



