268 PHYSIOLOGY OF ALIMENTATION. 



adequate to explain more than a few of the facts observed 

 experimentally in these fields. Perhaps pathology may also 

 find help here. 1 



6. Lipoidal Absorption. If a cell (such as a red blood- 

 corpuscle) possessing a semipermeable membrane is put into 

 a series of differently concentrated solutions of a certain 

 substance it will show no change in volume (will not shrink 

 or swell) in that solution which has the same osmotic 

 pressure as the cell contents. Such a solution is said to be 

 isosmotic or isotonic with the cell contents. If, now, solutions 

 of different substances are prepared a certain concentration 

 can be found for each of these in which the cell used for study 



1 On the hypothesis that oedema represents an increased affinity of 

 the colloids of the tissues for water brought about through the presence 

 in them of abnormal substances capable of increasing this affinity I 

 have made a series of experiments which seem to support this idea. 

 Not only does calculation show that the maximum amount of water 

 ever held by a tissue in cedema at no time exceeds the amount easily 

 absorbed by a gelatine plate, but acids and certain salts which increase 

 the affinity of gelatine plates for water increase in a similar way the 

 affinity of frog's muscles, connective tissue, etc., for water. In cedema- 

 tous tissues we have not only the presence of an increased amount of 

 CO 2 , but also organic acids of various kinds, and these present in con- 

 centrations which readily increase the affinity of ordinary gelatine plates 

 for water some 30 or 40 percent. Many poisonous substances such 

 as the irritant oils which by themselves do not increase the affinity 

 of a gelatine plate for water, nevertheless bring about an cedematous 

 swelling when applied to living tissues, apparently because they lead 

 to an altered metabolism of the cells concerned which brings with it 

 the production of substances which do increase the affinity of colloids 

 for water. An attempt to show that such substances are present in 

 cedenlatous tissues lead to the experiment of introducing frog's gas- 

 trocnemii into the peritoneal cavities of normal rabbits and rabbits with 

 an ascites due to the injection of uranium salts. In spite of the isoton- 

 icity of the normal and abnormal peritoneal fluids the frog's muscles 

 contained in the ascitic rabbits weighed 20 to 30 percent more at the 

 end of several days than those in the healthy rabbits. The blood-serum 

 of an ascitic rabbit will, moreover, upon injection, bring about an 

 oedema in a healthy one. 



