78 The Preparation of Microscope Slides 



quantities of the selected narcotic and then to fix the object at the exact 

 moment that it is completely narcotized but before it is dead. Many 

 marine forms, particularly sea anemones, may be narcotized by adding 

 small quantities of a saturated solution of magnesium sulfate to the water 

 in which they are expanded. There are, however, two mixtures that can 

 be recommended for general purposes. The first of these is: 



This is an excellent narcotic for small and delicate forms, such as 

 Rotifers and Bryozoa. About one drop per 10 ml should be added and well 

 mixed with the water in which the creatures are living. After about 10 

 min, further quantities may be added and left until narcotization is com- 

 plete. 



A useful narcotic for less delicate forms is: 



Gray's Mixture: 



Grind 48 g of menthol in a mortar with 52 g of chloral hydrate. 



This mutual solution of menthol and chloral hydrate is lighter than 

 water. A few drops placed on the surface of the water containing the 

 specimen dissolve slowly, allowing both constituents to act rapidly and 

 safely. This reagent is recommended for Coelenterates of all kinds. 



