20 DEVELOPMENT OF CEREBRO-SPINAL SPACES IN PIG AND IN MAN. 



IV. INJECTIONS AND REPLACEMENTS IN THE CEREBRO-SPINAL SYSTEM. 

 RESULTS OF REPLACEMENTS IN THE VENTRICULAR SYSTEM OF TRUE SOLUTIONS. 



The results of experiments carried out on embryo pigs by the technical pro- 

 cedures outlined in the previous section will be detailed here. The study was 

 made on this animal because of the facility with which it could be obtained living 

 and in good condition and also because it exhibits the characteristic meningeal 

 anatomy of all mammals. The chick could not be used in this investigation on 

 account of the dissimilarity between the avian and the mammalian meninges. 



The chief problem concerned here was the actual physiological extent of the 

 cerebro-spinal spaces. This apparently could be ascertained by the replacement of 

 cerebro-spinal fluid by the ferrocyanide mass. But there was also to be considered 

 the passage of fluid from the ventricles out into the periaxial* spaces, corresponding 

 exactly to a similar passage in the adult. 



If into the central canal of the spinal cord of a living pig embryo of 9 mm., 

 crown to rump measurement, an injection of the ferrocyanide solution be made 

 under very mild syringe-pressure, the ventricles can be fairly well rilled without 

 rupture of any element. Incubation of this experimental embryo with its circula- 

 tion continuing almost unabated for an hour should cause a further spread of the 

 fluid throughout the normal canals. If at the end of this time the whole embryo is 

 fixed in an acid medium the ferrocyanide will be precipitated in situ. 



Such a specimen, subsequently cleared by the Spalteholz method, is represented 

 in figure l.f In this drawing the spread of the injection solution is clearly shown. 

 Running upward from the point of introduction, wholly within the central canal of 

 the spinal cord, it reaches the bulbar region and extends outward into the large 

 fourth ventricle, appearing as a dense collection of the prussian-blue. Cephalad 

 from this region it spreads in diminishing intensity until it is finally lacking in the 

 diencephalon. 



The injected solution, then, in spite of the unavoidable increase in the normal 

 intramedullary pressure, is contained only within the medullary-canal system (cen- 

 tral canal of spinal cord and cerebral ventricles). There is no evidence of any 

 spread outwards, either from the third or fourth ventricle. 



In the next stage of meningeal development the replacement method can be 

 used, as the embryo is no longer too small for its employment. In figure 2 is repre- 

 sented an embryo of 13 mm., in which the circulation continued for 90 minutes 

 after the replacement. The same general picture shown in figure 1 results. The 

 whole medullary-canal system is filled with the precipitated prussian-blue, which 

 is densest in the region of the fourth ventricle. The roof of the ventricle, however, 

 shows a striking difference from that of the ventricle in the embryo of 9 mm. Just 

 posterior to the cerebellar lip is a regular oval, which is covered from within by a 

 dense collection of prussian-blue granules, causing it to stand out in clear contrast 

 to the thinner and more evenly distributed blue lining of the remainder of the 



*Throughout this paper the term "periaxial " has been used in the sense of "around the central nervous system " 

 or "around the eerebro-spinal axis." 



(Throughout this work the reference "figure " 1, etc., refers to plate illustrations; the word "text-figure" refers to 

 the illustrations inserted in the text. 



