STATIC TISSUES 2O; 



lusks, as Chiton, have analogous organs of touch on their shell-covered 

 surfaces. 



One other perceptory power must be considered here, and that is the 

 perception of heat and cold. Certain parts of the body surface in man 

 perceive very small differences of temperature, while others can only feel 

 much greater changes. When great extremes are properly applied, they 

 give the same result, a sense of intense cold, which means a destruction 

 of the organ and consequently of the power to perceive any heat. 



These sensory endings have not been discovered histologically. It 

 is possibly true that they are some of the same end-organs that also 

 perceive contact or other tactile stimuli. Or they may be specialized 

 to perform the thermo-perceptory function alone. It might prove pos- 

 sible to discover them by a process of comparison and elimination in 

 the various regions that possess them or do not possess them. 



Technic. The ordinary sectioning and staining methods are of no 

 value in the study of these tissues. Silver nitrate gives some good pictures 

 of the structure, but the methylene-blue method is the principal means 

 by which we have attained our present knowledge of their structure. 

 This method, we must repeat, is not one that cannot be learned out of a 

 book. The instructor must help and advise the student, and they must 

 adapt one of the numerous forms of this method, as set out in Lee, to 

 their needs. 



LITERATURE 



The literature is very large. Good papers may be found as follows : 

 RETZIUS, G. Papers in Biol. Untersuch., Jena. Last ten years. See Vol. 1902. 

 DOGIEL, A. S. Articles in the Arch, fur mik. Anal., Band XLIV, S. 15, Band XXXVII, 



S. 602, Band XLIX, S. 769, Band LII, S. 44, Band LIX, S. i. 

 HUBER, G. C. " Neuro-muscular Spindles in the Intercostal Muscles of the Cat," Am. 



Journ. of Anat., 1902, p. i. 

 PRENTISS, C. W. "The Otocyst of Decapod Crustacea," Bull. Museum of Comp. Zodl., 



Harvard, Vol. XXXVI, i 9 oi. 



THE TISSUES OF EQUILIBRATION OR STATIC TISSUES 



The static tissues or tissues of equilibration are tissues that record 

 the position of the body or some larger part of it with regard to gravity 

 or to the body's successive positions in space. It is impossible, some- 

 times, to differentiate between these two forms of the function; while 

 in other examples, very good evidence has been obtained to separate 

 them. These tissues appear as an epithelium. 



As has been said, this function must be looked upon as a very delicate 

 form of touch whose tissues are so placed as to perceive and record the 

 positions of small and heavy bodies which press or strike against them 

 by gravity, or, by inertia when the organism moves and changes its 

 position. The flow of fluids over the sensitive surface of some of the 



