444 Historical 



placed, from the physical and physiological points of view. The 

 passage below is truly very interesting: 



The diver is placed in a medium which compresses the whole 

 system. 



How does he get into equilibrium with these combined powers? 

 How can he surmount them? 



The logical solution is found in the characteristics and the prop- 

 erties of the vital force. It is necessary to consider in man what forms 

 the essence of life, that is, this energy which often modifies the laws of 

 nature, and reduces them to what they should be to constitute life; 

 it is the primordial law of the action, the conservation and the har- 

 mony of organized beings. 



Analysis does not permit us to resolve into its elements the nature 

 of this vital force attributed to a subtle, invisible spirit; but it is 

 enough that its existence should be proved by its properties, its con- 

 stant relationships. (P. 176.) 



To do justice to Brize-Fradin we must say that he is not satis- 

 fied with this vague declaration, and that, not content with meta- 

 physics, he tries to determine the effects of this vital force upon 

 the diver: 



The denser air, enclosed in the bell, brings to the lungs a greater 

 quantity of oxygen; immediately a greater quantity of heat is produced 

 there: this air, endowed with elastic force, rushes into the lungs; the 

 respiratory organ, the walls of which touch the pleura on all sides, 

 gains a greater capacity; the gas opens the angles which the vessels 

 form there and makes the passage of the blood through them freer 

 and easier; it increases the speed of the circulation, and multiplies in 

 the fibers of the muscles these inner frictions which are powerful 

 causes of heat. The levators and the intercostals contract quickly; 

 the ribs rise; the diaphragm falls; not only is the equilibrium de- 

 stroyed, but the elastic power of the air is repelled by this inner 

 energy which raises the muscular contractility to the highest degree, 

 and which follows the effects of the caloricity. 



We know that the pressure of the air upon a surface is equal to 

 a column of water thirty-one feet high; it has been calculated that 

 the effect of the pressure, in a man of average height, is equal to a 

 weight of 36,000; but this weight is counterbalanced by the vital force 

 and by the reaction of the elastic fluids which are part of our organ- 

 ism. Since the variations of the atmosphere are successive, they affect 

 us in a hardly perceptible way; but if a sudden change occurs, the 

 rupture of equilibrium has a very marked effect upon the animal 

 economy; if a man mounts to great heights, he experiences discomfort, 

 fatigue, drowsiness: so if we wish to account for the difference be- 

 tween the effects of the weight of water and those of the elastic force 

 of the compressed air at a depth of sixty feet, we must again resort to 

 this force whose principle is unknown, but which changes and modifies 

 the general laws, and puts into the class of demonstrated truths that 

 which at first glance seemed hard to explain. (P. 177.) 



