OF THE NERVOUS SYSTEM IN GENERAL. 467 



it becomes semi-transparent, plunged into water, it takes again 

 its colour and its opacity. 



747. The gray substance,* cinerea, called also cortical, 

 because it envelopes the preceding in many places, presents, 

 like it, and even still more so, varieties in shade: it varies 

 from lead gray to a blackish brown tint. This substance is 

 always softer than the white. The surface of its section is 

 uniform, and presents only points and red striae, more numer- 

 ous still than in the medullary substance. This substance, in- 

 deed, is, in some points at least, much more vascular than the 

 white. That which forms the cortical substance of the brain 

 and of the cerebellum contains so many vessels, that when it 

 has been well injected, and afterwards macerated, it appears 

 under the microscope entirely vascular. Albinus,t however, 

 affirms, and with reason, that in this case even there remains 

 one part evidently not capable of being injected, or extra-vas- 

 cular. The gray substance, submitted to the same chemical 

 preparations as the white, does not present an entirely similar 

 fibrous appearance on being torn. Submitted to the action of 

 water, the gray nervous substance becomes softer, swells a lit- 

 tle, and loses a great part of its colour. Acids, alcohol, and 

 especially corrosive sublimate, whiten it at the same time that 

 they render it harder; on being afterwards dried, it becomes 

 capable of being pulverized. The colour, a little variable ac- 

 cording to the races and individuals, appears to be a product 

 of the colouring matter of the blood. 



748. The two nervous substances are differently intermin- 

 gled with each other in the different parts of the nervous sys- 

 tem: in the lobes or hemispheres of the brain and cerebellum, 

 the gray substance forms an envelope or cortex to the white; 

 in the spinal marrow, the gray substance forms two interior 

 cords, enveloped by the white substance; in the medulla ob- 

 longata and in the crura cerebriand cerebelli, masses or nuclei 

 of the gray substance are found enveloped by the white, as 

 well as alternate layers of the two substances, cords or fibres 

 of both, which cross or traverse each other reciprocally; iti 



* Ludwig, de Cinerea cerebri substantia. 

 f dead, annot. lib. I. cap. 12. 



