434 JOTTINGS FROM SYDNEY UNIVERSITY BIOLOGICAL LABORATORY, 



shrinkage during the later processes which the specimens have to 

 undergo before reaching the strong alcohol stage. In the most 

 admirably fixed specimens shrivelling will often appear when 

 alcohol is applied. This difficulty is partly overcome, with great 

 pains, by using a series of alcohols of ascending degrees of strength. 

 But the result of this mode of procedure is not by any means 

 always satisfactory. 



Dr, Cobb, in a paper read before this Society,* has described a 

 method by which, in the case of small organisms, the shrinkage 

 due to change from one fluid to another of a different density may 

 be reduced to a minimum. In his differentiator we have an 

 instrument of admirable simplicity for ensuring this result. But 

 T have found that in practice the use of the differentiator involves 

 a considerable expenditure of time. To get a specimen from 

 distilled water to 90% alcohol for example, no fewer than eleven 

 different mixtures of water and alcohol have to be made up and 

 poured into the reservoir-tube. 



A simple piece of apparatus which I have devised does away 

 entirely with this — the gradual substitution for one another of 

 the two fluids of different densities being effected automatically. 

 An obvious mode of meeting the difficulty suggests itself at once. 

 Why not have the second fluid falling into the first drop by drop, 

 mixing thus very gradually with it and eventually replacing it ? 

 The difficulty in the way of this is that as each drop of the much 

 lighter liquid enters the denser, violent though circumscribed 

 currents are produced which are damaging to the delicate 

 organisms we are dealing with. 



The requisites for the method about to be described are — several 

 reservoirs of glass or earthenware fitted with glass taps and having 

 each a capacity of a gallon or more ; some wide-mouthed bottles of 

 a variety of sizes, fitted with perforated india-rubber stoppers, and 

 some lengths of glass and india-rubber tubing. 



Proceedings,' Vol. v., p. 157. 



