VASCULARITY IN THE NERVOUS SYSTEM 435 



A considerable number of different stains were tried, but none 

 were found to give a satisfactory contrast to the carmin gelatin 

 except the picric acid. Although this gave a rather poor differ- 

 entiation of the elements of the brain, it was found to be sufficient 

 for the identification of the various parts and was used entirely. 



In studying the sections, a square-ruled disc micrometer was 

 used in a Leitz ocular no. 3. The objectives employed were 

 Leitz nos. 3 and 7, and Bausch & Lomb 16 mm. and 4 mm. 

 The total length of the pieces of capillaries enclosed by the square 

 ruling (an area of 189 /z square under Leitz objective no. 7) in 

 each of ten sections was determined for each part studied in 

 every brain, and the ten results were added together, giving the 

 total length of the capillaries found in a block of tissue measuring 

 189 x 189 x 200 c. /*. In the cases where the thickness of the 

 sections was 15 n and where the Bausch & Lomb objective was 

 used, the results were corrected to correspond with this. 



There are several sources from which more or less serious 

 experimental error may arise in this method of investigation. 

 In the first place, there is the possibility of incomplete injection. 

 If all brains which show evidence of incomplete injection are 

 discarded, this source of possible error should not be serious 

 when a number of brains are used. 



While the fixation in Bouin's fluid causes relatively little 

 distortion, the complete technique employed does produce a 

 certain amount of shrinkage, as shown by Sugita and by the 

 observations recorded above. No effort was made to correct 

 for this, as it was considered that the relative vascularity of 

 different regions would not be affected by it, provided that 

 shrinkage is uniform throughout, as Sugita assumes to be the 

 case. The material fixed in formalin gave somewhat lower 

 results on the whole than the average values for the material 

 fixed in Bouin's fluid. This is shown graphically in chart 1. 



Any absolute determination of the vascularity by this method 

 is, of course, impossible, and the investigation seeks merely to 

 establish a set of ratios. 



Hill ('96) apparently showed that the quantity of blood in 

 the vessels of the brain when enclosed in the skull is practically 



