ALLEN: SENSORY FIBERS 15 



taminated mercury with cane sugar. After such a treatment 

 and a filtration through a pin hole the mercury comes out re- 

 markably clean. 



Unless the mercury has been partially purified in some manner 

 the tube A may become clogged by the accumulation of foreign 

 metals which concentrate in the tube as the mercury distils. 



If a wet process of purification has been employed, it is best 

 to dry the mercury by bubbling air through it for several hours 

 before introducing it into the still. 



After a distillation from this apparatus the mercury should 

 be given a filtration tlii'ough a pin hole in a filter paper in order 

 to remove a slight film of oxide produced by the oxidation of 

 metal impurities by the small amount of air remaining in the 

 still. After such a distillation and filtration the mercury may 

 be safely used in vacuum gages and in thermoregulators, and 

 for other purposes requiring a reasonably pure product. 



The yield of distilled mercury is about 400 cc. per twenty- 

 four-hour day, when the still is operated with a vacuum of 

 approximately 1 cm. of mercury. 



PHYSIOLOGY. — Sensory fibers in the mesencephalic root of man 



and the guinea pig. William F. Allen, Department of 



Anatomy, University of Oregon Medical School, Portland, 



/Oregon. 



As a result of Marchi stained serial sections of the brain stems 

 of a five year old girl and two guinea pigs, in which the left V- 

 roots of the guinea pigs were previously severed behind the 

 semilunar ganglion and the V-sensory root of the girl had been 

 destroyed by a large glioma in the pons region, the following 

 preliminary statement can be made: A number of sensory 

 fibers arising from cells in the semilunar ganglion follow the 

 ventral surface of the sensory root of the trigeminal nerve into 

 the brain stem to pass dorsally between the V-motor and the 

 V-sensory (substantia gelatinosa) nuclei to end in considerable 

 numbers in the motor nucleus. Other fibers continue dorsad 

 and cephalad in the V-mesencephalic root to terminate in the 



