HOW PLANTS AND ANIMALS GROW. 503 



ence in the same manner as upon a surface of water originally at 

 rest, and by continually uniting with the larger waves they 

 impart those dangerous qualities to the wave which result from 

 high and acuminate crests. 



When a film of oil is spread over the surface of the water, 

 this heaping-up action, which in the case of the water film results 

 in the formation of ripples, can not take place. In the figure, let 

 A represent the crest of a wave covered by 

 the film of oil B C, and let P be a point of 

 greatest action of the tangential force of 

 the wind, which is supposed to move in the 

 direction of the arrow. The tendency of Fig. 1. 



this action is to drive the film into a heap 



immediately in front of P. By this action a greater tension is 

 generated in the film at b and a lesser tension at a. The greater 

 tension at b tends to draw the portion at b' ahead, and the lesser 

 tension at a allows the tension at a' to draw the portion at a 

 ahead ; so that, instead of a tendency toward heaping up, there is 

 a tendency to move the entire surface film along at a uniform 

 rate. The formation of ripples is therefore stopped, and the 

 growth of waves and the formation of breaking crests, as far as 

 they result from this cause, are prevented. 



HOW PLANTS AND ANIMALS GROW. 



By Dr. MANLY MILES. 



TOO little is known in regard to the chemistry of foods, or the 

 specific use made of their proximate constituents in the pro- 

 cesses of nutrition, to serve as a rational guide in formulating 

 diets, or estimating the relative nutritive value of different arti- 

 cles of food. Our methods of chemical investigation are not as 

 yet sufficiently delicate and refined to enable us to trace the un- 

 obtrusive transformations of matter and energy involved in the 

 nutrition of living beings. 



Liebig's chemical theories of nutrition are now discarded by 

 physiologists as fallacious and misleading, but they are, neverthe- 

 less, confidently adopted by popular writers on the economy of 

 foods and diets, who are not aware of the progress made in a 

 more consistent knowledge of physiological processes. The his- 

 tory of biological science furnishes numerous instances of error 

 arising from the undue prominence given to non-essential details 

 which are readily observed, while the dominant factors in the 

 phenomena under investigation, which are not so obvious, are 

 overlooked or assigned a subordinate position. 



