196 PRACTICAL PHYSIOLOGY. [XXXIV. 



which moves it, and is then covered with a strip of paper, the 

 latter being laid on evenly to avoid folds, glazed side outermost. 

 One edge of the paper is gummed, and slightly overlaps the 

 other edge. Leave it for a few minutes until the gum dries. The 

 paper has then to be blackened, by holding the drum and keeping 

 it moving over a fan-tailed or bat's wing gas-burner, or paraffin 

 lamp — the former is preferable. Take care that the soot from 

 the flame is deposited evenly and lightly, and see that it is not 

 burned into the paper. The drum is then placed in position in 

 connection with its motor. (See Appendix.) 



To obtain a very fine film of soot, Hlirthle has invented a " smoke-spray." 

 The soot from the flame of a turpentine lamp is blown by 'means of an 

 elastic bail-bellows against the paper. 



3. General Rules for Graphic Experiments. 



(i.) Arrange the apparatus completely, cover the drum with 

 paper, and smoke it, before beginning the dissection. 



(2.) Test all the connections stage by stage as they are made. 



(3.) Each tracing is to be inscribed with the name of the 

 individual who made it, the date, what it shows, and then it 

 is varnished. 



4. Myographs. — Various forms are in use, but most of them 

 consist of a light lever which is raised by the contracting muscle, 

 and so arranged as to record its movement on a smoked surface of 

 paper or glass. Such curves are called " isotonic " by Pick. The 

 movements of the muscle are thereby magnified and rendered 

 visible to the eye. Or the lever may record its movements on a 

 moving surface. Taking advantage of the fact that a muscle when 

 it contracts becomes both shorter and thicker, myographs have 

 been constructed on three principles : — 



(a) Shortening of muscle attached to a lever. 

 (/5) Thickening of muscle on which the lever rests. 

 But suppose a muscle to be so fixed that during activity it cannot 

 contract, then we have changes »in tension, so that we can record 

 changes of tension bv the so-called "isometric " method introduced 

 by Fick (Lesson XXXVL). 



(y) Changes in tension. 

 The recording surface on wliich the style of the lever writes may 

 be— 



(i.) Stationary (PJlw/er^s). 

 (2.) Rotatory (Helmholtz's). 

 (3.) Swinging pendulum (Fick^s). 



(4.) Moved from side to side by a spring, either vertically (Du 

 Bois~Reymo)id) or horizontally. 



