162 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



of the globulins, and not a true coagulation process. He does not appear to 

 have investigated the question of a specific myosin ferment. 



When a muscle is gradually heated, at a certain temperature it contracts 

 permanently and loses its irritability. This phenomenon is known as heat- 

 rigor, and is due to the coagulation of the proteids in the muscle. If a 

 tracing is taken of the shortening, it is found that the first shortening occurs 

 at the coagulation temperature of paramyosinogen (47°-50° C), and if the 

 heating is continued a second shortening occurs at 56° C, the coagulation 

 temperature of myosinogen. If frog's muscles are used there are three 

 shortenings — namely, at 40°, 47°, and 56° C. ; frog's muscle thus contains 

 an additional proteid which coagulates at 40° C. (T. G. Brodie). Von Fiirth 

 regards this additional proteid as the soluble myosin alluded to above, some 

 of which in frog's muscle is present before rigor mortis occurs. 



In addition to all the proteids previously enumerated, there is a small 

 quantity of nucleo-proteid. 



NERVOUS TISSUES 



The chemical investigation of nervous tissiies does not lend itself very 

 well to class exercises ; still it may not be uninteresting to state briefly the 

 principal known facts in relation to this subject. The most important points 

 which any table of analyses will show are : (1; the large percentage of water, 

 especially in the grey matter ; (2) the large percentage of proteid. In grey 

 matter, where the cells are prominent structures, this is most marked, and 

 of the solids, proteid material here comprises more than half of the total. 

 The following are some analyses which give the mean of a number of 

 observations on the nervous tissues of human beings, monkeys, dogs, and 

 cats : 



The most abundant proteid is nucleo-proteid; there is also a certain 

 amount of globulin, which, like the paramyosinogen of muscle, is coagulated 

 by heat dt the low temperature of 47° C. A certain small amount of neuro- 

 keratin (especially abundant in white matter) is included in the above table 

 with the proteids. The granules in nerve cells (Nissl's bodies), which stain 

 readily with methylene blue, are nucleo-proteid in nature. Tlie next most 

 abundant substances are of a fatty nature ; the most prominent of these is 

 the phosphorised fat called lecithin (see p. 18). In the nervous tissues 

 lecithin is combined with cerebrin to form a complex substance called 

 protagon, which crystallises out on cooling a hot alcoholic extract of brain or 



