432 THE EXPERIMENTAL PRODUCTION OF AN INTERNAL HYDROCEPHALUS. 

 THE REACTIONS OF THE EXPERIMENTAL ANIMALS. 



Age is apparently a determining factor in the reactions of an animal after the 

 intraventricular or subarachnoid injection of lampblack. Probably more important 

 than the actual age of the animal is the associated degree of ossification of the 

 skull; if the union between the bony plates is marked and firm, the increase in 

 intracranial tension does not result in any enlargement of the bony skull. This 

 enlargement of the head, met with in kittens after the subarachnoid or intraven- 

 tricular injection of suspensions of lampblack, seems to be compensatory in nature 

 and allows much more cerebral function than is possible in an adult animal with a 

 rigid skull. The experimental findings in the immature and in the adult animals 

 will in consequence be detailed under separate headings. 



KITTENS. 



In all, 35 kittens were given subarachnoid or intraventricular injections of 

 suspensions of lampblack. These kittens were from 18 litters and at the time of 

 experimentation were normal, healthy animals. The age at the time of experi- 

 mentation ranged from 24 hours to 42 days. The younger animals were all being 

 taken care of by the mothers, whereas the older in the series were being fed as 

 adults. 



As the technical procedure of injection was very simple, practically none of 

 the animals died acutely as the result of the experiment. Of the 35 kittens used, 

 8 died (or were sacrificed because of poor physical condition) within the first 8 

 days; 8 survived for more than 4 and less than 10 days; and the remainder (19) 

 lived for over 10 days. The longest period of survival after the experimental injec- 

 tion was 47 days. The cases considered to be most successful and showing most 

 pronounced enlargement of the head were those which lived more than 14 days 

 after the experimental injection. The number of the animals in the series surviving 

 for several days is really surprisingly large, and the proportion of early deaths, con- 

 sidering the age of the animal at the tune of the experiment, was very low. 



No real or essential difference between the reaction of the kittens receiving 

 subarachnoid or intraventricular injections could be made out. Possibly, those 

 receiving the lampblack into the subarachnoid space showed enlargement of the 

 head somewhat more rapidly and remained in better physical condition for a longer 

 period. By both routes, however, the production of an internal hydrocephalus 

 seems equally certain, provided a suitable dose (best, about 1.0 c.c. of a 10 per cent 

 suspension) of lampblack be given. The release of cerebro-spinal fluid by needle 

 through the occipito-atlantoid ligament is much more certain than is ventricular 

 puncture through the fibrous fontanelle or through the thin bone of a young kitten. 

 Pathologically, there is practically no difference in the hydrocephalus resulting 

 from either procedure; the amount of carbon particles found in the cerebral ven- 

 tricles is, however, much smaller in the animals receiving the occipito-atlantoid 

 injection. In these experiments the most extreme cases of internal hydrocephalus 

 have been those produced by such subarachnoid injection. Of 35 animals, 19 were 

 given intraventricular and 16 subarachnoid injections. 



