6 MAN, — THE ANIMAL 



were discovered with the progress of research, 

 eventually, by common approval, the statements 

 were raised to the rank of laws of life. At the 

 end of this long testing, it is easily understood why 

 such laws are regarded as the foundations of our 

 uncertain superstructure of the theories concerning 

 man. 



In gaining the facts which constitute the basis 

 for the generalizations of life, biology has not 

 worked apart from other sciences. The physics of 

 optics as applied to the perfecting of lenses in 

 microscopes has been of indispensable value in 

 furthering an accurate knowledge of minute struc- 

 tural conditions in protoplasm. While the appli- 

 cation of chemical methods to certain phases of 

 vital phenomena has cast a flood of light on the 

 obscure relations of heat and energy in living 

 things, it is probably correct to say that bio- 

 chemistry has done more to advance our knowl- 

 edge of nutrition, respiration and body heat in the 

 past fifteen years than in the preceding fifty years. 

 These discoveries enable one to write with much 

 more definiteness than ever before. We thus come 

 to realize that the generalizations about life de- 

 pend not only on the work of many persons but 

 also upon the best that the related sciences have 

 to offer. 



We would not have you think for a moment 

 that all of the problems connected with the funda- 



