THE EXPERIMENTAL PRODUCTION OP AN INTERNAL HYDROCEPHALUS. 429 



But when consideration is given to the enlargement of the lateral ventricles 

 from obstruction to flow within the meninges, a plausible explanation is more 

 difficult. The mere mechanical explanation does not fairly meet the question as to 

 why the meningeal block does not cause compression of the cerebral cortex, dila- 

 tation of the subarachnoid spaces, and a typical external hydrocephalus. In one 

 variety of this type (obstruction at the foramina of the fourth ventricle) the mechan- 

 ical explanation holds. But actually, a diffuse block to the outflow of cerebro- 

 spinal fluid within the meninges results almost inevitably in the later production 

 of an internal hydrocephalus. 



Clinically, a differentiation between the two types of internal hydrocephalus 

 may be made. In children Gushing (1908) found that the cerebral ventricles of 

 one kind of internal hydrocephalus (due to block in the meninges) could be drained 

 by lumbar puncture, while in the other (due to block in the ventricular system) 

 the cerebral ventricles could be emptied only from the ventricular needle. Similarly, 

 Dandy and Blackfan (1913, 1914) recovered by lumbar needle phenolsulpho- 

 nephthalein injected into the cerebral ventricle in the "communicating" type, while 

 the subarachnoid absorption was markedly retarded. In the obstructive type these 

 writers showed a negligible absorption from the cerebral ventricles, but an unim- 

 paired absorption from the subarachnoid space. In these cases the dye injected 

 into the dilated ventricles did not appear as normally in the lumbar fluid. 



Experimentally, the obstructive type of hydrocephalus alone seems to have 

 been produced. Dandy and Blackfan (1913, 1914) were able to cause a typical 

 internal hydrocephalus in dogs by two methods, the first of which gave the patho- 

 logical picture of an intraventricular block. Pledgets of cotton were introduced 

 from the occipital region through the fourth ventricle into the aqueduct of Sylvius. 

 Such a foreign obstruction caused signs of cerebral pressure (lethargy, vomiting) 

 and a rather acute dilatation of the ventricles was produced. In a somewhat 

 different way the same enlargement of the ventricles was accomplished by ligation 

 of the vein of Galen, but this occurred in only one of the ten animals used. In the 

 other nine animals the higher ligation apparently permitted sufficient collateral 

 circulation. Dandy and Blackfan used young dogs 2 to 6 months of age; at this 

 time in the dog the cranial sutures are strongly united, so that no enlargement of 

 the head occurred. The time allowed for the dilatation of the ventricles varied from 

 three to eight weeks after the operation. At the end of this period a fair degree of 

 hydrocephalus was present. 



At about the same time Thomas (1914) published the results of his experiments 

 on the production of an internal hydrocephalus by the intraventricular injection 

 of aleuronat in starch. This protein caused a marked inflammatory reaction, 

 blocking finally the ventricular pathway at one or other of the narrow parts. Dogs 

 were used throughout for the observations. Thomas found little enlargement of 

 the ventricles present in the first week, but in the chronic stage of the inflammatory 

 process incited by the protein, an internal hydrocephalus developed, with symp- 

 toms of increased intracranial pressure. The dilatation of the lateral ventricles 

 occurred slowly and reached its maximum in about two months. Subsequent intra- 



