40 THE PREPARATION OF THE JELLY FILM 



to the proper one in the resultant jelly with which the 

 film is made. It is imperative to explain the way in 

 which the jelly is made even at the risk of being 

 verbiose. Bear in mind, therefore, that two solutions are 

 required namely, No. 1, a stock 2-per-cent solution 

 of agar, and No. 2, a solution which contains the 

 other substances the effects of which are to be tried on 

 the cells. Solutions Nos. 1 and 2 are always mixed 

 together in equal parts and then boiled up to form 

 No. 3, from which the jelly-film on the slide is prepared. 

 No. 1 is always the same. No. 2 may contain a variety 

 of substances, but no matter how much of any sub- 

 stance No. 2 may contain, No. 3 will always have half 

 that amount. For example, if one wishes a cell to rest 

 on a jelly containing 1 per cent of morphine one must 

 have 2 per cent of morphine in No. 2, so that when the 

 two solutions are mixed in equal parts the combination, 

 that is No. 3, will contain 1 per cent of morphine. 



A word is necessary as to the effects on cells of the 

 agar itself. It appears to be innocuous. We have tried 

 it in strengths double and even four times as great as 

 that contained in the stock solution, without apparently 

 producing any deleterious effect upon the vitality of 

 the cells experimented with. 



