178 PKEPAKATION AND MOUNTING 



as Nelson's or Cox's : some persons of experience prefer the 

 latter. 



10. Colours. The size-solution above mentioned will 

 need some colouring matter to render it visible when in- 

 jected into the vessels of an animal, and different colours 

 are used when two or more kinds of vessels are so treated, 

 in order that each set may be easily distinguished by 

 sight. The proportion in which these colours are added to 

 the size-solution may be given as follows : 



11. For 



Bed 8 parts of size-solution 



(by weight) to 1 part of vermilion. 



Yellow ... 6 ,-, 1 chrome yellow. 



White ... 5 1 flake-white. 



Blue 3 1 blue-smalt, fine. 



Black ...12 1 lampblack. 



Whichever of these colours is used must be levigated in a 

 mortar with the addition of a very small quantity of water 

 until every lump of colour or foreign matter is reduced to 

 the finest state possible, otherwise in the process of injecting 

 it will most likely be found that some of the small channels 

 have been closed and the progress of the liquid stopped. 

 When this fineness of particles is attained, warmth sufficient 

 to render the size quite fluid must be used, and the colour 

 added gradually, stirring all the time with a rod. It may 

 be here mentioned that where one colour only is required, 

 vermilion is, perhaps, the best ; and blue is seldom used 

 for opaque objects, as it reflects very little more light than 

 black. 



12. When it is wished to fill the capillaries (the minute 

 vessels connecting the arteries with the veins), the Micro- 

 graphic Dictionary recommends the colouring matter to bo 

 made by double decomposition. As a professed handbook 

 would be, perhaps, deemed incomplete without some direc- 

 tions as to the mode of getting the*e colours, I will here 



