WASTE PRODUCTS. 115 



which a portion of the cells of the body act for the whole, 

 but it is not a new function, but, a function that has become 

 specialized ; for in the unicellular forms we have motion 

 without muscular fibre. 



So we might go on showing that the so-called specialized 

 functions are more highly developed attributes that are to be 

 found in unicellular life. But this is unnecessary. 



Waste products may be divided into two classes : the 

 respiratory and the urinary. The respiratory product is 

 always rich in oxygen, while the urinary product is always 

 comparatively poor in oxygen. This distinguishing feature 

 remains constant for all forms of life, whether animal, vege- 

 table, or the lower forms, that are so doubtful that some have 

 thought it well to create for them a separate department. 



The waste products of the animal forms are sufficiently 

 well-known. The consideration of them has been entered 

 into by every author who has written on the subject of 

 physiology; and is therefore unnecessary here. I will, 

 however, call attention to some important facts that will 

 be of use in the consideration of the variations observed 

 in the waste products of some of the lower forms of life. 

 There is, perhaps, no part of the animal frame that is abso- 

 lutely constant in its chemical components. All are subject 

 to variations within certain limits that are by no means well 

 defined. So it is with the waste products. While they are 

 constant in their general characters, they are subject to varia- 

 tions with changes in the character of the food employed by 

 the animal. For instance, if my urine is acid to-day, I may 

 render it alkaline to-morrow, or next day, by eating a few 

 oranges or lemons. The small amount of the alkaline base, 

 combined with the acids of the fruit, is sufficient to bring 

 about this change, while the acid itself is destroyed by remo- 

 leculization. This instance is doubly instructive, for if we 

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