BOILTXO WATER AND ROTIFERS. 307 



whiter, and on the third day they were in a very desirable condi- 

 tion. But what was I to do with them now ? 



I placed a few in a watch glass and added osmic acid. It 

 certainly fixed them, but they lost their natural transparency, the 

 ganglionic region became contracted as by a rope, the cilia were 

 unsatisfactory, and the trophi and intestines not very clear.* I 

 tried others with corrosive sublimate, which seemed to darken 

 them and affect them more or less like osmic acid. Next I 

 experimented with tannic acid (lo per cent, in water), and found 

 that the cilia stood out very clearly, whilst the rest of the body 

 became blurred and tanned. Picro-sulphuric acid fixed only a 

 few specimens satisfactorily, whilst chloral hydrate, acetic acid, 

 alcohol, and chromic acid were likewise more or less unsatisfac- 

 tory. I also experimented with chloroform, and found that, after 

 allowing them to revive, they would never re-expand, their tails 

 swimming about in a contracted or crippled form, in which condi- 

 tion they were, of course, useless. 



This was the whole list of fixing fluids that I was practically 

 acquainted with, and as none had given me entire satisfaction in 

 the above experiments, 1 looked about for some others. I happen- 

 ed to go to my chemical press to review the list of all the deadly 

 poisons at my command, when I heard the tea-kettle singing 

 cheerfully on the kitchen fire, and at once I thought of making 

 use of the boiling water. Quickly I got half a dozen tumblers 

 with concave bottoms i7i the inside^ poured about 3 or 4 tea- 

 spoonfuls of the water containing the starved Rotifers into each 

 tumbler, and next poured quickly and suddenly a solid stream of 

 boiling water into each tumbler. I let the water cool, gave it then 

 a circular motion by passing a pencil around the inside of each 

 tumbler, as this gathered all the killed organisms into the centre 

 of the concave bottom, and then examined a drop of the sedi- 

 ment in a watch-glass. 



My surprise was immense. The trochal disc was better 

 defined than with any chemical excepting tannic acid ; the trophi 

 were quite clear, also the oesophagus, stomach, gastric glands, 

 ovary, contractile vesicle, and foot-glands. The longitudinal 

 muscles stood out clear like polished ropes, while the vascular 

 system could be easily traced. The ganglionic ring was indistinct, 



