AND EMBRYOLOGY OF FKOGS. 393 



day the inner membrane begins to swell, due to a slow osmotic 

 action, I think, as the membrane is stretched by tension from 

 within. On the third or fourth day the swollen membrane may be 

 pierced by a sharp needle, and the egg taken out, which is then 

 placed permanently in 80 per cent, alcohol. The method is ex- 

 ceedingly simple, and consists largely in waiting a few days for the 

 osmotic action to take place. Such eggs, if properly prepared, 

 are in excellent histological condition. This simple method has 

 proved so successful that I have not further experimented with it. 

 It is possible that it may be improved by varying the strength of 

 alcohol used, but I have not seen the need of looking further. The 

 membrane does not swell in stronger alcohol than 70 per cent., 

 and weaker would macerate the eggs. 



Certain precautions are necessary in embedding the eggs to 

 prevent brittleness. This is obviated by soaking the eggs before 

 embedding for several hours in a solution of turpentine saturated 

 with paraffin, and kept in a warm place — not so hot as the water- 

 bath (5o°C.) Heat causes the eggs to become brittle. This is 

 obviated by the above process of soaking, so that the egg need not 

 remain so long as an hour in the melted paraffin of the water-bath. 

 In the younger stages there is no need for very thin sections, but 

 sections to^u. thick are sufficient for all purposes. If the sections 

 are cut too thin, the yolk tends to break up and crumble. 



Sterilisation of Water. — An important communication 

 has been made to the Paris Academy of Medicine concerning the 

 different methods employed to obtain water free from living organ- 

 isms. This result is very difficult to obtain except by boiling the 

 water, and this plan is objectionable on account of the insipidity 

 of the liquid thus deprived of its dissolved gas. Filters of every 

 description fail to remove the whole of the germs, and, unless 

 carefully and frequendy cleaned, may even add to the number 

 naturally existing in the water. After studying the numerous pro- 

 cesses in vogue, the investigator decided to adopt a similar plan to 

 that by which suspended minute particles in water are precipitated. 

 The specimen to be purified was first shaken with powdered alum 

 and then left to rest for twenty-four hours. When that time had 

 elapsed the water was perfectly clear, and was also found to be 

 almost completely sterilised. Freshly-prepared sulphate of cal- 

 cium, oxide of iron, and sulphate of iron are also fairly effective 

 in producing the same result. 



