61 EECORD OF CURRENT RESEARCHES RELATING TO 



alcohol by sucking out the water with blotting-paper, by which means 

 the zoospores are killed suddenly. The alcohol is then replaced by 

 water, and that by saturated carmine. At the end of some minutes 

 the latter is sucked out by blotting-paper, and replaced by Avater, and 

 that finally by crystallized acetic acid which instantaneously clarifies 

 the objects. There can then be seen in the rostral region of the 

 zoosj)ores a small spherical nucleus coloured an intense red and very 

 clearly defined, the rest of the body remaining very pale. As acetic 

 acid is very volatile, it is only necessary to place at the side of the 

 cover-glass a drop of glycerine, which penetrates and replaces the 

 acid which has evaporated, preserving the form of the zoospores ; a 

 preparation is thus made which on being sealed down will be 

 permanent. 



For the zoospores of the CEdogonium the process is somewhat 

 difi'erent ; they are killed by exposing the drop of water for a minute 

 to the vapours of a 1 per cent, solution of osmic acid, and then 

 cemented beneath the cover-glass by paraffin, coloured by carmine, 

 and clarified by acetic acid and glycerine ; the action of the carmine 

 should be more prolonged than with the alcohol method. The 

 nucleus, situated at the median region of the body rather nearer the 

 posterior end, appears as a small sphere coloured red. 



These zoospores were killed during their period of mobility — the 

 nuclei could not be confused with the amylaceous corpuscles which are 

 met with in many of the Volvocineas by the side of the true nucleus, 

 as the corpuscles are never coloui'ed red in preparations prepared as 

 above — we have therefore a true nucleus combined with vibratile cilia 

 and contractile vacuoles. 



The two algae studied have zoospores of two different types, those 

 of Microspora being flagellated, and of CEdogonium furnished with a 

 crown of vibratile cilia, and M. Maupas is persuaded that if the 

 zoospores of other algse are examined they will all be found to have 

 a nucleus. 



MICEOSCOPY, &c. 



Corrosion as a Histological Method.*— The process of corrosion 

 has been applied with considerable success to anatomical preparations. 

 Dr. Eichard Altmann, of Geissen, now proposes to apply the process 

 to the investigation of certain microscoi)ical structures. 



The method adopted is, in the first place, to impregnate the tissue, 

 or to inject its vessels, with olive or castor oil, then to place it in 

 osmic acid until the oil is hardened and blackened, and finally to 

 transfer it to a solution of potassium or sodium hyjwchlorite (eau de 

 Javelle), which completely destroys the tissue, the fatty material being 

 left, and retaining the form of the vessels or spaces into which it was 

 injected. 



Thin membranes may be placed, immediately after injection, into 

 osmic acid, but as that reagent has very little penetrating pov/er, large 

 organs have to be frozen, thin sections of them cut, and these sections 



* ' Airh. Mikr. Anat.," xvi. (1879) p. 471. 



