994 



THE CENTRAL NERVOUS SYSTEM 



to litmus, and with a specific gravity of about 1004 to 1007. It 

 contains the ordinary salts, but more potassium than sodium, unlike 

 other body fluids; a very small amount of protein (globulin) 

 usually about o-i per cent. and a little dextrose (Nawratzki). 

 Its composition is evidently different from that of ordinary lymph. 

 Only a few lymphocytes are present in health, but in some diseases 

 (as in general paralysis of the insane, tabes, and cerebro-spinal 

 syphilis) a marked increase occurs. In acute cerebro-spinal menin- 

 gitis numerous polymorphonuclear leucocytes are found, which are 

 absent from the normal fluid. 



The depression of the freezing-point (A) usually lies between 

 0-60 and 0-65 C. In a case of hydrocephalus it was 0-65 C. 

 Normally, cerebro-spinal fluid ,is somewhat hypertonic to the blood- 



Fig. 400. Sagittal Section of Dog's Skull, showing the Needle introduced into Third 

 Ventricle to tap Cerebro-Spinal Fluid (Weed and Gushing). 



serum. In injury of the cribriform plate of the ethmoid bone and 

 also in some cases where there is no traumatic injury, the fluid 

 escapes from the nose, and the rate of its formation can thus be 

 ascertained. In one case it was found to be as much as 2 c.c. to 

 nearly 4 c.c. in ten minutes. 



PRACTICAL EXERCISES ON CHAPTER XVI. 



i. Section and Stimulation of the Spinal Nerve-Roots in the Frog. (a) 



Select a large frog (a bull-frog, if possible). Pith the brain. Fasten 

 the frog, belly down, on a plate of cork. Make an incision in the middle 

 line over the spinous processes of the lowest three or four vertebrae, 

 separate the muscles from the vertebral arches, and with strong scissors 

 open the spinal canal, taking care not to injure the cord by passing the 

 blade of the scissors too deeply. Extend the opening upwards till two 



