948 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



hydroxide when thrown into water. When a substance breaks down into 

 simpler bodies through absorption of water the process is called hydrolysis or 

 hydrolytic cleavage. Thus cane-sugar may take up water and be resolved into 

 a mixture of dextrose and levulose, which are called cleavage-products. So, 

 likewise, starch and proteid are resolved into series of simpler bodies through 

 hydrolytic cleavage changes which take place in intestinal digestion. All 

 forms of fermentation and putrefaction are characterized by hydrolysis (exam- 

 ples, p. 944), and hence complete drying prevents such processes. Alcoholic, 

 butyric, and lactic fermentation are apparent though not real exceptions to the 

 above. Alcoholic fermentation, for example, is usually represented by the 

 reaction, C 6 H 12 O 6 = 2C 2 H 5 OH + 2CO 2 , but the CO 2 is in fact united with 

 water, and hence the true reaction should read, 



C 6 H 12 6 + 2H 2 = 2C 2 H 5 OH + 2H 2 CO 3 . 



Sugar. Alcohol. 



Drinking-water contains salts and air dissolved, giving it an agreeable taste. 

 One does not willingly take distilled water on account of its tastelessness. 

 Drinking large quantities of water produces a slight increase in the decom- 

 position of proteid in the body. 



Dry animal membranes and cells absorb water in quantities varying with the concentra- 

 tion and the quality of salts in the solution in which they are suspended (Liebig). This is 

 called imbibition. Membranes will absorb a solution of potassium salts in greater quantity 

 than of sodium salts, and so the potassium salts are found predominating in the cells, the 

 sodium salts in the fluids of the body. A blood-corpuscle treated with distilled water 

 swells because it can hold more distilled water than it can salt-containing plasma. A cor- 

 puscle placed in a 0.65 percent, solution of sodium chloride (the physiological salt-solution) 

 remains unchanged, for this corresponds in concentration to the plasma of the blood. If 

 the corpuscle be placed in a strong solution of a salt it shrivels, because it cannot hold as 

 much of that solution as it can one having the strength of the salts of the plasma. Oysters 

 are often planted at the mouths of fresh-water rivers, since they imbibe more of the weaker 

 solution and appear fatter. If salt be placed on meat and left to itself, a brine is formed 

 around the meat, not on account of the hygroscopic properties of the salt, but because 

 salt penetrates the tissues, which can then hold less water than they could before, and 

 so water is forced out from the meat. 



Diiferent bodies require different quantities of heat to warm them to the same extent. 

 The amount of heat required to raise the temperature of water is greater than that for any 

 other substance. A calorie or heat-unit is the amount of heat required to raise 1 cubic 

 centimeter of water from to 1 C. The specific heat of the human body that is, the 

 amount of heat required to raise 1 gram 1 C. is about 0.8 that of water. On the trans- 

 formation of a substance from the solid to the liquid state, a certain amount of heat is 

 absorbed, known as latent heat. To melt 1 gram of ice producing 1 gram of water at 0, 

 79 calories are required, or sufficient to raise 1 gram of water from to 79. Upon the 

 basis of these facts a determination may be made by means of the ice-calorimeter of the 

 number of heat-units produced in the combustion. For example, 1 gram of sugar (dex- 

 trose) burned in an ice-chamber, melts 49.86 grams of ice. Since each gram required 

 79 calories to melt it, 3939 calories must have been produced altogether. If I gram of 

 sugar be burned in the body, the heat produced is identically the same, and may be meas- 

 ured with great accuracy. 1 



In the transformation of water at 100 to steam at 100 there is a further absorption of 



1 M. Rubner: Zeitschrift filr Biologie, 1893, Bd. 30, p. 73. 



