THE EXPERIMENTAL PRODUCTION OF AN INTERNAL HYDROCEPHALUS. 441 



the constant secretion of fluid by the cells and the consequent washing-off of any 

 lodging particles. On this hypothesis, which seems justified, the production of 

 cerebro-spinal fluid by the ependyma must be negligible. 



The gross pathological features, then, of the central nervous system of a kitten 

 receiving intradural injection of lampblack are those of a typical internal hydro- 

 cephalus, such as is clinically quite common in children. The dilatation of the 

 cerebral ventricles thus produced experimentally has been extreme. 



ADULT CATS. 



The same pathological dilatation of the lateral ventricles has been produced 

 by this means in adult animals, but the degree of dilatation is far less than in 

 kittens. This is in large part to be accounted for by the fact that in these adult 

 animals enlargement of the bony skull is impossible and the compression of the 

 cortex, through dilatation of the ventricles, is associated with the physiological 

 limit of increase in intracranial pressure and its consequent bulbar effects. Bitem- 

 poral decompressions might possibly allow greater ventricular enlargement and a 

 longer period of survival for the animal. 



But by such injections of lampblack an obvious and considerable dilatation of 

 the lateral ventricles is effected (figs. 1 and 3). The lateral ventricles in the most 

 extreme cases have become dilated to 7 to 8 mm. in transverse diameter an 

 enlargement comparable to those illustrated by Thomas (1914) and by Dandy and 

 Blackfan (1913, 1914), though occurring in a shorter period. The dilatation is for 

 the most part a symmetrical process and is confined at first, or in the less extreme 

 cases, to the body and frontal prolongation of the cavity. In the more striking 

 cases the temporal prolongation is found dilated and the enlargement is traceable 

 into the posterior horn. Such changes in ventricular capacity are wholly similar 

 to the internal hydrocephalus developing clinically in man after obstruction to the 

 pathways of the cerebro-spinal fluid. One receives the impression that the changes 

 in the very old cats are not as marked as those occurring in the young adults. 



The thinning of the cortex in these adults is, of course, not marked, and is 

 dependent upon the dilatation of the ventricles ; for the reduction in thickness of the 

 cortex is not, under these experimental conditions, in any way primary but is second- 

 ary. The differentiation between gray and white matter is not lost, even in these 

 formalinized specimens (fig. 3). 



In the adult animals the suspension of lampblack, when introduced into the 

 cisterna cerebello-medullaris by occipito-atlantoid puncture, finds its way into the 

 lateral ventricles in rather small amounts. The chief distribution of the granules 

 after such injection is into the spinal and basilar subarachnoid spaces. The lamp- 

 black after a massive injection is found frequently in rather large amount in the 

 temporal process of the lateral ventricle; in these cases the dilatation has not been 

 great. The comparative freedom of the choroid plexuses from the granules, pointed 

 out in kittens, has been noted in the adults. 



Pathologically, the degree of dilatation of the lateral ventricles following 

 subarachnoid injections of lampblack has been somewhat variable (cf. figs. 1 and 3). 



