288 ANNUAL OF SCIENTIFIC DISCOVERY. 



Leaving electricity on one side, and dealing, therefore, only 

 with heat and work as the "actual" forces set free during con- 

 traction, the above exijeriments clearly lead to the conclusion that 

 the sum total of the forces becoming "actual" during contraction 

 depends on, is a function of the tension of the muscular fibre 

 (before and) during that act. Ilcidenhain obtained similar re- 

 sults in experimenting with tetanus. To say that the sum total 

 of forces set free during contraction is influenced by the tension 

 of the fibres, is, of course, to say that tlie quantity of latent energy 

 consumed, the amount of chemical actioi^ concerned in the act, is 

 influenced by the same means. AVe ought, therefore, to find an in- 

 crease of waste products in muscles which are made to contract 

 under tension. Taking one such waste product as an index of the 

 others, Ilcidenhain satisfied himself not only that there was a pro- 

 duction of carbonic acid during contraction, but also, that the 

 amount of it was in proportion to the sum total of force becoming 

 " actual," and was a function of the tension of the fibres. 



Tliat the mere, so to speak, physical extension of a muscular 

 fibre should have a marked influence on the metamorphosis of its 

 substance, has been for a long time practically admitted, though 

 the matter had never been rigidly ascertained before the investi- 

 gations of Heidenhain. The subject is not lacking in practical 

 importance ; but it is chiefly of interest, inasnmch as it bears 

 very closely on the general theory of muscular action, — Reader. 



SOURCE OF MUSCULAR POWER. 



Twenty years ago, physiologists would have attributed the 

 source of muscular power to something peculiar, developed by 

 living animals, and termed vital force. The progress of scientific 

 discover}', however, rapidly dissipated the very crude notions 

 which then existed regarding this mysterious agency. We now 

 know that an animal, howe\er high its organization may be, can 

 no move generate an amount of force ca])able of moving a grain 

 of sand than a stone cau fall upward, or a locomotive dri\e a 

 train without fuel. All that such an animal can do is to liberate 

 that store of force, or potential energy, which is locked up in its 

 food. It is the chemical change which food suffers in the body of 

 the animal that liljcrates the previously pent-up forces of that 

 food, which now make their appearance in the form of actual 

 energy, — as heat and mechanical moti<m. From food, and food 

 alone, comes the matter of which the animal body is built up ; and 

 from food alone come all the different kinds of physical force 

 which an animal is capable of manifesting. 



The two chief forms of foi'ce thus manifested are heat and mus- 

 cular motion, or mechanical work. These have been almost uni- 

 versalh' traced to two distinct sources, — the heat to the oxidation 

 of the food, and the mechanical work to the oxidation of the 

 muscles. This doctrine, first promulgated by Liebig, has been 

 "within late years adopted by most physiologists, and has been 

 taught in all the text-books treating of the subject. The proxi- 

 mate constituents of food have been frequently divided into two 



