the Blood in Muscular Work. 17 



the oxidation is intra- or extravascular. This consequently has 

 to be decided on other grounds ; and the evidence in favour of 

 the view that the oxidation takes place outside the capillaries 

 preponderates greatly. In muscle, besides the proper muscular 

 fibre with its connective tissue and the capillaries, there is an in- 

 terstitial fluid (the " muscular juice "), which Claude Bernard 

 calls the "milieu" of the fibre, and which may be regarded as 

 a medium common to the fibre and the vessel. On the one 

 hand, it is by the reaction between the fibre and this fluid 

 which surrounds and saturates it that the chemical change takes 

 place (oxidation or its equivalent) by which the force is evolved ; 

 on the other hand, this fluid being separated from the blood only 

 by the thin capillary wall, the most perfect equalization of their 

 diffusible constituents must take place by osmosis, oxygen pass- 

 ing from the blood into the interstitial fluid, and products of 

 oxidation from this fluid into the blood ; so far, then, as the sup- 

 ply of oxygen is concerned, the muscular juice is equivalent to the 

 blood. Were intravascular oxidation the source of muscular 

 force, the evolution of the force must cease absolutely on the 

 supply of blood being cut off. We find, on the contrary, that a 

 muscle continues to contract for some time after its removal from 

 the body, showing that force (or, in other words, oxygen and 

 oxidizable material) is stored up in the muscle ; and it is further 

 found that after frequent and sustained contraction the muscular 

 juice is changed in composition. We find, again, that muscular 

 contractility survives removal longest in cold-blooded animals, 

 whose blood contains a minimum of oxygen; and when a 

 warm-blooded animal is brought into a state analogous to that 

 of reptiles, its blood being rendered venous and its tempera- 

 ture greatly lowered, its muscles also retain their contractility, 

 as has been shown by Claude Bernard'' s "lapin a sang froid/' in 

 which the above conditions are induced by section of the cervical 

 spinal cord. It is perhaps scarcely necessary to notice a difficulty 

 in the hypothesis of Professor Heaton; but it might fairly be 

 asked how force evolved within the capillary is transmitted to 

 the "comparatively distant fibre 5- ' by which it is manifested. 



Oxidation has been spoken of in this discussion as the source 

 of muscular work without any qualification ; but it should be 

 understood that there is an essential difference between the mode 

 of oxidation which yields the animal heat, and that which affords 

 mechanical work or nerve-force. While heat is evolved continu- 

 ously and uniformly, nervo-muscular action takes place inter- 

 mittently, abruptly, and with varying intensity on the application 

 of a "stimulus/'' i. e. the oxygen and oxidizable matter being in 

 presence, the combination only occurs when some impulse is 

 given. It is thus not a simple case of combination of oxygen 



Phil Mag. S. 4. Vol. 38. No. 252. July 1869. C 



