566 WILLIAM PATTEN. 



or saflPronine is the best, since the sections can be cut a little 

 thicker, and still be transparent enough to show the cell 

 structure. This proved of great advantage, since in the early 

 stages the sections, if cut too thin, were liable to crumble on 

 account of the abundance of yolk. When the eggs were 

 stained with hsematoxylin they were allowed to remain in the 

 staining fluid for five or six days, and were then decolorised 

 very gradually in an extremely weak solution of alcohol and 

 hydrochloric acid — one drop of strong acid to about twenty 

 grammes of alcohol — in which they are allowed to remain several 

 days, and then transferred to pure alcohol, which is changed 

 once or twice until the object has regained its violet colour. 

 Out of a cluster containing about one hundred and twenty-five 

 eggs, only one half or even less could be properly stained. 

 Some were stained only on the outside, although appearing as 

 dark as the rest. By the process of decolourising, such eggs 

 were easily detected and picked out. Some eggs stained more 

 rapidly than others ; by leaving them five or six days in the 

 fluid, such as could be at all afi'ected were over-stained. When 

 placed in the solution of hydrochloric acid, all were decolourised 

 alike. The eggs were next transferred successively into abso- 

 lute alcohol, clove oil, and paraffine, remaining several hours in 

 each. 



In treating subsequently the eggs of Blatta some changes 

 were made which proved of great advantage. Benzole was 

 used in the place of clove oil ; it rendered the eggs transparent 

 almost instantly, and since it is more fluid than clove oil, there 

 is much less danger of the embryo being shrivelled, while at 

 the same time the yolk is not made so hard and brittle. 

 After remaining in benzole for half an hour, the eggs are 

 changed to a saturated solution of benzole and paraffine, 

 which, when allowed to evaporate slowly, gives a perfectly 

 transparent and tolerably hard paraffine. They are next trans- 

 ferred to melted paraffine, which at once replaces the benzole 

 expelled by the heat. Thus there is a great saving of time, 

 since clove oil is not thoroughly replaced by paraffine in less 

 than five or six hours, while with benzole one half-hour is 



