APPARATUS FOR PHYSIOLOGICAL USE. 251 



processes (among which may be mentioned specially those 

 of the nervous system), are at present out of the reach of 

 investigation. All that we can do is to stand on one side 

 in the attitude of attentive observers. Investigation is 

 impossible because we cannot do that which constitutes an 

 experiment, we cannot modify at will the conditions under 

 which the phenomena occur. As regards other processes 

 our position as investigators is more favourable, and no 

 better example can be given than that of muscular action. 

 We can determine beforehand the conditions of an experi- 

 ment, with as much exactitude as the physicist can in his 

 investigations of the processes of the non-living world. I 

 will illustrate this by a final example. We have here 

 some ice, of which I will put a fragment near the muscle, 

 of which we have already investigated the mode of con- 

 traction, and again record on the cylinder a series of 

 contractions. The result is well worthy of your attention. 

 Under the influence of cold, you will see that the process 

 is completely modified. The curve of contraction, before 

 so uniform, assumes, as the living substance of the muscle 

 is gradually cooled, an entirely different character. Its 

 function, however, though modified is not impaired. The 

 proof of this lies in the fact that if the bit of ice is now 

 removed, and the observation continued, it will gradually 

 return to its former condition, i.e. the curve of its contrac- 

 tion will again present its normal contour. 



