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



salts immediately precipitated as prussian-blue. The purpose of these observations 

 was solely to ascertain the effect of injections at pressures above the normal tension, 

 so that the conclusions drawn from the replacement method might be more fully 

 substantiated. 



It was soon ascertained that the pressures caused by injections with a simple 

 syringe could be fairly well controlled and that several degrees of tension might be 

 employed. Thus it was found to be simple and serviceable to designate the injec- 

 tions as those made with mild, moderate, or strong syringe-pressure. Most of these 

 injections were made into the central canal of the spinal cord, but occasionally into 

 the perispinal spaces or cerebral ventricles. Injections under equivalent pressures 

 in the central canal of the spinal cord or into the cerebral ventricles always gave 

 corresponding results. It is necessary to record that the injections, even under 

 strong pressure, were not carried to the point of macroscopic rupture. 



The so-called mild syringe-pressure, making use of solutions of potassium ferro- 

 cyanide and iron-ammonium citrate, resulted in extensions of the prussian-blue 

 wholly similar to those obtained in the replacement experiments which were carried 

 on for 30 minutes and over. This similarity indicates a complete filling of the avail- 

 able cerebro-spinal system in the replacement method, for certainly (even in the 

 mildest syringe injections) the intra ventricular pressure must be excessively 

 increased. Figure 1 shows a specimen under such conditions, with a marked thin- 

 ning of the injection mass in the region of the fore-brain. This finding is customarily 

 present in the injections under mild pressure, due to the pushing upwards of an 

 existent ventricular fluid. 



When moderate pressures are employed with the syringe the picture gradually 

 changes. The essential difference in the results obtained by moderate syringe 

 injection and by the replacement method lies in the greater extension of the foreign 

 solution in the smaller embryos. Thus in figure 9 the spread of the injection 

 precipitate in a pig embryo 16 mm. is shown to be about as extensive as that obtained 

 by the replacement method in an embryo of 19 mm. (fig. 5). The extra ventricular 

 distribution of the injected solution around the medulla, the extension (even more 

 marked here) along the central roots of the caudal cranial nerves, and the localized 

 perispinal spread are easily made out in this specimen of 16 mm. 



This general rule applies to all of the results obtained with the use of syringe- 

 pressures above the mildest. Dependent upon the degree of syringe-tension, the 

 spread extends in simple ratio. Thus, by the use of moderate pressures of injection 

 into the central canal of the spinal cord, a complete intramedullary and periaxial 

 spread was secured in a pig embryo of 22 mm. somewhat earlier than the equivalent 

 stage was ob tamed by the use of the replacement method. 



With the highest syringe-pressures (insufficient, however, to cause macroscopic 

 rupture) the same general type of injection spread was obtained, bringing the more 

 complete stages down into smaller and smaller embryos. Most of these embryos, 

 however, on microscopic section showed obvious rupture of some part of the central 

 nervous system. 



