THE MICROSCOPE IN BIOLOGY. 117 



tion of an immaterial animating principle or soul (ammo], 

 all vital functions are produced. The vis medicatrix na- 

 turce of Cullen was an attempt to compromise between 

 the rival theories of a superadded principle and a special 

 activity in organized matter itself.* 



Harvey, Hunter, Miiller, and Prout proposed hypotheses 

 similar to those of Aristotle and Hippocrates, and many 

 modern scientific men accept similar views. The recent 

 doctrine of the correlation of physical forces has, however, 

 revived the mechanical and chemical theories, and the 

 industry with which these view^s have been propagated 

 has gained many adherents. 



It is to be regretted that philosophy should assume the 

 name of science and dogmatize under that appellation. 

 The object of science is to state facts, and not to dream, 

 yet such is the nature of man's intellect that it will seek 

 to account for facts, and is thus drawn into metaphysical 

 speculation. If the age-long controversy between the 

 physicists and the vitalists is ever to cease, it will prob- 

 ably be through the microscopic demonstration of the 

 absolute difference between living and non-living matter. 



In the present chapter it is designed to set forth briefly 

 the principal facts of elementary biology as they have 

 been brought to light by microscopy. For further illus- 

 trations in vegetable and animal histology, reference may 

 be made to following chapters. 



1. All biologists agree that the elementary unit in living 

 bodies is the cell. This, according to the most recent in- 

 vestigations, is a soft, transparent, colorless, jelly-like par- 

 ticle of matter, which may be large enough to be just dis- 

 cernible to the naked eye, or so small as to be invisible 

 with our best instruments. The simplest or most elemen- 

 tary forms of vegetable or animal life consist of single 

 cells, while the more complex organisms are built up of 



* Compare Bostock's History of Medicine. 



