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



have exerted a more potent action on the structures constituting the lower area of 

 fluid passage. 



Another interesting phenomenon of the injections of silver nitrate is shown in 

 figure 12. The embryo of 13 mm. here represented was injected under strong 

 syringe-pressure with a solution of silver nitrate into the central canal of the spinal 

 cord. On subsequent reduction and clearing it was found that the excessive pressure 

 had resulted in a complete intramedullary injection with a localized pedunculate 

 spread into the tissues from the roof of the fourth ventricle. This bulbous extrava- 

 sation into the extraventricular tissue has not been observed in any specimens except 

 those into which the solution of silver nitrate was injected. Such a spread is prob- 

 ably to be accounted for by an immediate coagulation of the surrounding tissue. 



The extensive use of solutions of silver nitrate as a means of demonstrating 

 vascular channels naturally suggests a careful comparison of the results obtained 

 from its use and those obtained from the employment of other available true solu- 

 tions, in regard to the evidence afforded by the two methods of intraspinous injec- 

 tions. The chief objection to the use of silver nitrate, as has already been mentioned, 

 is its power to coagulate protein. This is illustrated by many features of the 

 specimen shown in figure 11 by the sharp outlining of the area of fluid passage, the 

 markings on the caudal process of the fourth ventricle, and the delimitation of the 

 cerebellar lip. But much more marked are the evidences of this coagulative power 

 as shown in figure 12, the pedunculated extraventricular spread, the transverse 

 corrugation of the cerebellar lip (amounting to circumscribed indentations), and the 

 peculiar outlining of the roof attachment to the bulb. These phenomena obtained 

 by the intraspinous injection of solutions of silver nitrate must be classed as arti- 

 facts. The different degrees of this corrosive action of the silver probably result 

 from the varying rates of reduction of the salt to the metal, a factor which is not 

 easily regulated. The findings, therefore, with this method are worthless unless 

 controlled. 



Many embryos of varying sizes were injected with the silver nitrate. In the 

 main these observations followed the course of development of the cerebro-spinal 

 spaces as evidenced by the replacement experiments with the ferrocyanide. The 

 injections required moderate pressure in the syringe in order to secure more than a 

 local extension from the roof of the fourth ventricle, and to secure the same extent 

 of spread it was generally necessary to use embryos a few millimeters larger than 

 those required in the replacement experiments; but this is to be expected, in view 

 of the probability of a constant precipitation of the albuminous tissues by the 

 injection fluid. 



Specimens prepared by the intraspinous injection of silver nitrate, then, afford 

 but little reliable evidence in this problem except of a substantiative sort. The 

 findings by this method indicate that the perispinal and pericerebral spaces, in pig 

 embryos of 25 mm. and upward, could be filled by an injection of silver nitrate under 

 moderate pressures into the central canal of the spinal cord. The point of pas- 

 sage of the fluid from the intramedullary to the periaxial system was in the region 

 of the roof of the fourth ventricle. 



