THE EXPERIMENTAL PRODUCTION OF AN INTERNAL HYDROCEPHALUS. 433 



On recovery from the ether, these experimental kittens with subarachnoid or 

 intraventricular injection can hardly be told from the normal control animal in the 

 litter. If abnormal at all, they tend to be somewhat less active in crawling about 

 and seem cautious in movements, particularly in regard to the head. The next 

 morning the experimental animal usually did not differ from the control, though a 

 slight carefulness and slowness in reaction might be present (noted in 5 out of 16 

 cases). On the second morning, in the more pronounced cases of obstruction, an 

 enlargement of the head has been made out; this is usually demonstrated by the 

 formation, again, of suture lines previously closed. In other cases no signs of an 

 incipient hydrocephalus were definite until the fourth morning, and this may be 

 considered to be the usual interval before the pathological change may be made 

 out. Thus, aside from a slight initial slowness in reaction, it may be assumed that 

 no abnormalities are apparent until the lapse of sufficient time for the increase in 

 intraventricular tension to cause enlargement of the head. 



As soon as definite changes in the size of the anterior fontanelle and in the 

 widening of the sutures have appeared, the further enlargement of the head pro- 

 gresses with a fair degree of rapidity. In those kittens in which injection has not 

 been made until after bony union of the cranium has occurred, there is a definite 

 diastasis of the bones with the forming anew of fibrous sutures and fontanelles. 

 This opening-up of the bony skull has been observed in 5 kittens, the ages at the 

 time of injection varying from 17 to 42 days. In general, however, these experi- 

 ments have been performed on animals in which the closure of the skull was incom- 

 plete; the enlargement of the head could be brought about by dilatation of the 

 existing fibrous sutures. 



This enlargement of the head is of amazing rapidity and degree. In these 

 experimental cases, as in man, the increase in size is practically entirely confined 

 to the cranial vault, while the base of the skull remains fairly constant. Such 

 enlargement of the vault naturally causes separation merely of the flat bones of the 

 calvarium and leaves unchanged the relative positions of eyes and ears. 



The subsequent clinical course of the experimental kittens was largely 

 influenced by the factors mentioned. The weaker kittens soon reached a stage 

 when the head became too heavy for them to lift, so that progression was accom- 

 plished by pushing the head along the floor of the cage. In others, the increasing 

 weight of the head could be handled more easily, though most of these showed an 

 ataxia more profound in degree than usual for kittens of equal age. Many of these 

 kittens with enlarged heads remained very active even after two weeks; one in 

 particular continued to climb with great facility upon the perpendicular wire side 

 of the cage. In general, however, it must be granted that the kitten receiving the 

 lampblack was more cautious and more sluggish in reaction than the control. The 

 animals of the same litters subjected to subarachnoid or intraventricular injections 

 of cinnabar could not be distinguished from normal. 



The cause of death in the animals was variable, though two agencies were 

 responsible for the majority. In the first place, death of the kittens from infection 

 with B. bronchisepticus was unfortunately very common; the bronchial pneumonia 



