BY DR. MICHAEL FOSTER. 397 



monin, and bring the closed bottle immediately under it. The 

 muscle exhibiting no contractions (there being no escape of 

 ammonia), slip away the glass cover from the top of the bottle ; 

 contractions will at once follow. 



In the above observations, a fresh surface of muscle must be 

 cut after each trial, as the body used as stimulus destroys the 

 layer of muscle with which it is immediately in contact. 



Apply the substance under trial as soon as possible after 

 making the section, as the surface exposed soon dies. 



IV. Chemical Stimulation of Nerve. 06s. VII. Pre- 

 pare a nerve-muscle with as long a piece of nerve as possible. 

 Fasten the muscle in the clamp, and support the nerve so that 

 the end hangs freely down in a vertical position. Bring a drop 

 of one of the below-mentioned fluids, on a glass plate, in con- 

 tact with the end of the nerve, allow some millimetres at least 

 of the nerves to be fully immersed in the fluid ; and either take 

 a fresh nerve-muscle for each experiment or cut away each 

 time all that portion of the nerve which had been previously 

 exposed to the action of the fluid. 



The movements of the muscle may be recorded as usual, 

 not load the muscle with anything more than the lever 



elf. 



The following substances applied to a nerve produce con- 



aotions in its muscles : 



Mineral acids, in considerable concentration only; neutral 

 suits of the alkalis and metallic salts, in considerable concen- 

 tration only; lactic acid, only when concentrated; glycerin, 

 only when concentrated. 



Ammonia hardly acts at all as a stimulus to nerve ; in 

 making trial with this, care must be taken to protect the 

 muscle from all ammonia vapor. 



V. Thermal Stimulation of Muscle. Obs. VIII. Hav- 

 ing arranged a sartorious muscle, as in Obs. V., bring to the 

 lower cut surface a thin slip of heated metal. On contact 

 taking place, a contraction will result. In this case the heat 

 is applied to a part only of the muscle. 



06s. IX. Attach a gastrocnemius to a lever (either with 

 the origin of the muscle downwards and the tendon upwards, 

 or in the ordinary position with the tendon playing round a 

 pulley) in such a way that flic whole muscle may readily be 

 immersed in fluid. Fig. 202 represents a convenient arrange- 

 ment for this and other purposes. The muscle a is fastened 

 to the clamp c, which is part of the bent holder d. This 

 holder moves on the same upright as the lever e. The tendon 

 of the muscle is attached by the thread b to the lever, so that 

 its contractions pull the lever down. The lever is counter- 

 balanced by weights carried over a pulley. The muscle can 

 thus be readily immersed in or withdrawn from any fluid. 

 Counterbalance the lever with 10 or 15 grammes. 



