No. 582] SIGNIFICANCE OF INTERNAL CONDITIONS 341 



It is probable that an organ or organs having a glyco- 

 genic function exist in some invertebrates, e. g., the 

 oyster, since glycogen may be obtained from these ani- 

 mals. Whether such a delicate adjustment similar to 

 that obtaining in the higher animals between stored glyco- 

 gen and circulating carbohydrate exists in these forms is 

 unknown to us. 



5. The Osmotic Pressure of the Body Fluids 

 In many species of homoiothermal animals, the osmotic 

 pressure of the blood, as measured by the depression of 

 the freezing point, is very constant, nor can it be easily 

 influenced by changes in the environment. The ingestion 

 of large quantities of water may he followed by the secre- 

 tion of large quantities of dilute urine or by profuse per- 

 spiration. A shortage of water to drink leads to the se- 

 cretion of small quantities of more concentrated urine. 

 Both qualitatively and quantitatively, the physico-chem- 

 ical constitution of the blood varies within relatively nar~ 

 row limits. 



6. The Digestive Tract „ 

 The mechanical and chemical processes of the alimen- 

 tary tract reduce all the food, or its digestible portions, 

 to water-soluble substances, in which form they are ab- 

 sorbed. The proteins of the food are reduced to the 

 amino acids or polypeptids, the starches and sugars to 

 monosaccharides and the fats to soaps before being ab- 

 sorbed. 



The introduction of foreign proteins, e. g., egg albumen, 

 as such directly into the blood of the host is injurious. 

 But the amino acids and polypeptids to which this pro- 

 tein is hydrolyzed by the action of the digestive enzymes 

 are, in general, qualitatively the same as those in the blood 

 of the host. The difference in proteins depends upon the 

 difference in the quantitative relations of the amino acids 

 in the protein molecule as well as upon the qualitative 

 differences. The hydrolysis of all proteins to their 



