82 THE NATURE AND ORIGIN OF LIFE 



same dimension as life. But what is the dimension of life ? 

 We know that vital phenomena are at once colloid and 

 chemical ; in our experiments, therefore, we shall have to 

 use colloid reagents and purely chemical reagents ; and we 

 shall make still surer that we are using reagents really of the 

 same dimension as life if we use living reagents. 



The number of experiments made in the past twenty years 

 by this method of hypodermic injection of well-determined 

 reagents into living animals is something tremendous. It 

 is safe to say that in no branch of science has like activity 

 been shown ; and the results have been in proportion. 

 Even from the practical point of view this line of research 

 has given us vaccination and serumtherapy and birth to 

 scientific medicine. 



We have said that experiments should be made with 

 chemicals, with colloids, and with living substances. The 

 results obtained by means of the two latter groups of sub- 

 stances are by far the most important. Those due to the 

 injection of a non-colloid solution of chemical substances, 

 such as the injection of alkaloids or of chemically defined 

 salts, concern us much less ; they tell us nothing new and 

 only verify the law of habit. This would seem to prove that, 

 while life is at once colloid and chemical, it is, if I may say 

 so, more accessible to experiment on the colloid side. We must, 

 therefore, apply ourselves chiefly to experiments having to 

 do with the injection of living or not-living colloids in order 

 to establish the simple laws we seek. 



