File:Weed1917 plate01.jpg

Plate I. Pig Embryos 9 to 14.5 mm

Fig. 1. Drawing of a pig embryo of 9 mm, into the spinal central canal of which an injection of 0.5 per cent solution of potassium ferrocyanide and iron-ammonium citrate was made under very mild syringe-pressure. The embryo was fixed in Camoy's fluid to which 1 per cent hydrochloric acid had been added. The specimen was carefully dehydrated and cleared by the Spalteholz method. The resultant precipitate of prussian-blue is found w holly within the central canal of the spinal cord and within the cerebral ventricles. Enlargement, 11 diameters.

Fig. 2. Drawing of a pig embryo of 13 mm, in which the cerebro-spinal fluid was replacc<l by a 1 per cent solution of potassium ferrocyanide and iron-ammonium citrate. The embryo was kept alive for 90 minutes after this replacement and was then fixed in 10 per cent formol containing 1 per cent hydrochloric acid, .\fter dehydration the specimen was cleared by the Spalteholz method. The occiurence of a definite oval, outlined by the denser mass of the granules, in the roof of the fourth ventricle, is characteristic of this stage. Enlargement, 9 diameters.

Fig. 3. Drawing of a pig embryo of 14.5 mm, in which the cerebro-spinal fluid was likewise replaced by the ferrocyanide solution, After the replacement, the embryo was kept alive for 60 minutes; it was fixed in Camoy's fluid (with 1 per cent hydrochloric acid added) and after dehydration it was cleared by the SpaltehoU method. The earliest indications of a peria.idal spread of the replaced fluid from the roof of the fourth ventricle is here shown. Enlargement, 8 diameters.

Reference

Weed LH. The development of the cerebro-spinal spaces in pig and in man. (1917) Contrib. Embryol., Carnegie Inst. Wash., 5, No. 14 .