442 THE EXPERIMENTAL PRODUCTION OF AN INTERNAL HYDROCEPHALUS. 



A moderate injection of a 10 per cent suspension yielded in 5 days considerable 

 ventricular enlargement (fig. 1), while the 5 per cent suspension gave in 16 days 

 but little (fig. 3). Comparable subarachnoid injections of cinnabar and of lyco- 

 podium spores caused no obvious abnormality in ventricular capacity (figs. 2 and 4) . 



DISCUSSION OF RESULTS. 



The production of a typical internal hydrocephalus in kittens and adult cats 

 by the injection of lampblack into the normal pathways of the cerebro-spinal 

 fluid invites question as to the exact mechanism by which this enlargement of the 

 ventricles is brought about. In both kittens and adult cats the condition has been 

 caused by the injection of a suspension of these carbon granules through the occipito- 

 atlantoid ligament into the cisterna cerebello-medullaris. The distribution of 

 these granules subsequently is largely within the basilar and spinal subarachnoid 

 space, with a smaller spread over the cerebral and cerebellar cortices. The maximal 

 aggregation of granules is in the peribulbar cisterns with a minimal concentration 

 within the ventricles. Following the intraventricular injection, as used in some of 

 these kittens, the distribution of granules is largely intraventricular, basilar, and 

 spinal, with but a small amount over the cerebrum. The same pathological picture 

 in the main results from both types of injection. 



After such experimental procedures there is usually a distinct interval of time 

 between the initial injection and the appearance of signs indicative of intracrania 

 pressure. In adult cats, this interval is usually of 6 or more hours. In very old 

 cats, however, there seems to be really no time interval; the obstruction to flow 

 seems complete enough to induce immediately a state of lethargy. This interval 

 in kittens, however, is prolonged to 24 hours or more; usually enlargement of the 

 head can be noted only after the fourth day. 



It becomes necessary to reconcile, if possible, these somewhat divergent time- 

 intervals and to attempt the formulation of an hypothesis to meet the conditions. 

 The almost immediate appearance of a lethargy in very old cats indicates that 

 at least a partial obstruction of the cerebro-spinal fluid is caused by the mere col- 

 lection of these granules in the subarachnoid space. The fact that these older 

 animals show symptoms immediately may be due to a decrease in the power of the 

 medulla to resist alterations in pressure in the subarachnoid space. The increase in 

 this pressure must be acute in all of the animals, but it seems likely that the obstruc- 

 tion to flow is only partial and that with a slightly increased head of pressure the 

 fluid is forced through the incompletely occluded channels. 



Subsequently, another factor seems to play a role and the blockage becomes 

 apparently more complete. Two explanations for the formation of this obstruction 

 may be offered: The first concerns the definite aggregation of the granules into a 

 fairly impervious, impenetrable mass, mechanically hindering the flow of cerebro- 

 spinal fluid. This probably plays a part in the initial blocking of the channels, but 

 some other influence is doubtless necessary to render the aggregation of granules 

 more impervious to fluid. This second factor is very likely the reactive phenomenon 

 on the part of the body to the presence of such foreign granulation. Such a reaction 



