LECTURE IV 

 ON SOME PHYSICAL MANIFESTATIONS OF LIFE 



i. f HYPOTHESES OF MUSCULAR CONTRACTION 



THE phenomena which allow us to discriminate between dead and 

 living matter are physical processes, e.g. in higher animals, the contraction 

 of the heart, the respiratory and other muscular motions. If the chemi- 

 cal processes in living matter and the physical changes they bring about 

 in the colloids were entirely known, the physical manifestations of life 

 would also be clear to us. The periodic character of many of the mani- 

 festations of life suggests the idea that these processes occur in several 

 phases which are probably connected, partially at least, in a catenary 

 way, so that the preceding process has effects which cause the subse- 

 quent phase of the process. 



These catenary mechanisms are for the most part still unknown. 

 Inasmuch as the number of possible changes in the condition of colloids 

 seems limited, the impression might be gathered that by a guess the 

 whole secret of the physical manifestations of life might be unraveled. 

 Such surmises find their way occasionally into print. As a rule, those 

 who are familiar with the specific case for which the guess is made are 

 not helped by it. It is not worth while to devote any time to the point- 

 ing out of the futility if not open absurdity of most of these attempts. 



The origin of animal heat from chemical energy offers no further 

 mystery. We know that a kilo of sugar yields about four thousand 

 calories of heat, if burned in the laboratory, and that it gives the same 

 heat if oxidized in the body. In our modern theory of nutrition, the 

 heat value of the various kinds of food is justly used as the basis for 

 the calculation of their nutritive value. The times are gone when physi- 

 cians and biologists dared to raise the objection as they did against 

 Robert Mayer that our body inherits its heat. 



As far as the transformation of chemical energy into mechanical 

 energy in the muscle is concerned, Robert Mayer and Helmholtz con- 

 sidered the muscle as a thermodynamical machine. They assumed 

 that in the muscle the heat produced by chemical processes is partly 



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