ANIMAL FLUIDS AND TISSUES. 665 



organic matter contained in it. Its average composition may be thus 

 stated : 



Water and organic matter 3,5 



Calcium phosphate and traces of fluoride .... 86.9 



Magnesium phosphate 1.5 



Calcium carbonate ........ 8.0 



Tartar is the name given to the substance which deposits from 

 alkaline saliva on the teeth. It is of a grayish, yellowish, or brown- 

 ish color, and consists chiefly of calcium phosphate, with a little 

 carbonate, but contains also bacteria and other organic matter, salts 

 of the alkalies, and silica. 



Hair, nails, horns, hoofs, feathers, epithelium, are nearly iden- 

 tical in composition. They all contain cholesterin and nitrogenous 

 substances termed keratins, which are probably not distinct chemical 

 compounds, but mixtures of several substances similar in composition 

 and properties. 



Cholesterin fats are very resistant to the action of putrefactive bacteria, and 

 the occurrence of these fats in combination with the keratins serves as a pro- 

 tection to the skin surface from the attacks of the ever-present bacteria. 



Muscle. The chemical composition of the various morphological 

 elements of striated muscle is not definitely known. Fresh, inactive 

 muscle has an amphoteric reaction i. e., it colors red litmus-paper 

 faintly blue, and blue litmus-paper slightly red. After activity or 

 death the reaction becomes acid. If the blood is removed from 

 muscle immediately after death, and the muscle is then quickly cut 

 and frozen, an alkaline fluid can be pressed out, the muscle-plasma, 

 which contains the proteins of muscle. Muscle-plasma coagulates 

 spontaneously, separating a protein body, myosin, and yielding a 

 serum, muscle-serum. A similar change takes place in the muscle 

 shortly after death, causing the hardening of the muscle observed in 

 rigor mortis. 



The more important constituents of muscle are considered here 

 without attempting a morphological distinction. 



Proteins of muscle. There is at present no generally accepted view 

 as to the nature of the essential proteins of muscle tissue. This is 

 due largely to the many different names given them, which are in 

 almost hopeless confusion. It seems certain that there are at least 

 two proteins in living muscle which have the power of coagulating 

 after death. V. Fiirth calls the less abundant of these myosin and 

 its coagulated form myosin fibrin ; the second he calls myogen, and 



