VITAL PHENOMENA. IQI 



§ I. Extrinsic Conditions. 



Extrinsic Conditiofts. — By showing that every vital 

 manifestation results from the conflict of two factors : 

 the extrinsic or physico-chemical conditions which 

 determine its appearance, and the intrinsic or organic 

 conditions which regulate its form, Claude Bernard 

 dealt a mortal blow at the old vitalist theories. For 

 he has not only asserted the close dependence of the 

 two kinds of factors, but he has shown them in action 

 in most physiological phenomena. The study of the 

 extrinsic or physico-chemical conditions necessary to 

 vital manifestations teaches us our first truth — 

 namely, that they are not infinitely varied as might 

 be supposed. They present, on the contrary, a 

 remarkable uniformity in their essential qualities. 

 The fundamental conditions are the same for the 

 animal or vegetable cells of every species. They are 

 four in number : — moisture, the air, or rather oxygen, 

 heat, and a certain chemical constitutioji of the medium, 

 and the last condition, the enunciation of which 

 seems vague, becomes more precise if we look at it 

 a little closer. The chemical constitution of media 

 favourable to life, the media of culture, obeys three 

 general laws. It is the knowledge of these laws 

 which formerly enabled Pasteur, RauHn, Cohn, and 

 Balbiani to provide the media appropriate to the 

 existence of certain relatively simple organisms, and 

 thus to create an infinitely valuable method for 

 the study of nutrition, etc., — namely, the method of 

 artificial cultures, numerous developments of which 

 have been shown us by microbiology and physiology. 

 The Optimum Laiv. — It has been said, and it is 

 more than a play on words, that the conditions of 



