120 VITAMINS A AND CAROTENES 



arachnoidal villi (Figs. 31, 32, and 33). The production of vitamin A defi- 

 ciency is, in the opinion of the writer, an easy and accurate method of 

 determining the sites of arachnoidal villi which vary in different species. 

 In the spinal canal, deficiency of vitamin A results in overcrowding of its 

 contents. Those dorsal and ventral nerve roots in the rat and guinea pig 



Fig. 31. Vitamin A deficiency in the rat. Brain of a 9-vveek-old rat which liad 

 shown paralysis for 16 days. Herniations (H) of cerebrum and cerebellum into the 

 transverse sinuses and confluens sinuum. Note flattening of the cerebellum where it 

 was forced into the foramen magnum. 



which arise distal (caudad) to the midthoracic region and leave the spinal 

 canal at lower levels (lumbar and sacral) become too long for the inter- 

 vertebral distances between levels of origin and exit. The result is buckling 

 and herniation into intervertebral foramens and into posterior root ganglia 

 (Fig. 34). Buckling of nerve roots on the ventral side of the spinal cord 

 causes pressure atrophy of l^one and herniations into the bodies of verte- 

 brae (Fig. 35). In rat, guinea pig, and chick, -^■■' appositional growth (if bone 



29» Since the com|)leti()n of this mniniscript , studies Ikiac been published on the 

 effects of vitamin A deficiency and iiy|)(Mvit;iniinosis A on chicks and ducks. Re- 



