MCINTOSH, ON YOUNG SALMON. 145 



light ; a third neutral tint, not ground, for use when the 

 light has to be purified or subdued, but not diffused. The 

 advantage of being able to bring any one kind of modifica- 

 tion into play during an observation is great, whilst being 

 always at hand the apparatus is likely to be employed, to the 

 immense comfort of the observer, especially by artificial 

 light. 



Lamp-light may be diffused by means of a small globe. The 

 following plan, however, has certain advantages. Grind one 

 side of the chimney itself at its lower part near the flame, 

 which may easily be done with a piece of wetted sandstone. 

 A strongly illuminated area of small extent is thus available 

 as the source of light, when the breadth of the flame is not 

 sufficient ; while, by half a revolution of the chimney on its 

 support, the uncovered flame may be instantly substituted 

 whenever it is to be preferred. 



Experiments on Young Salmon.* 

 By W. C. McIntosh, M.D., F.L.S. 



Early in 1862, and in the winter of 1862-3, the develop- 

 ment of numerous salmon ova was observed, and some 

 experiments performed on the young fish. Unfortunately, 

 these had to be laid aside in March, 1863, for more pressing 

 engagements, with the intention of again resuming them on 

 a favorable opportunity; but since this has not occurred, the 

 results — such as they are — are now briefly narrated. I may 

 likewise state that during the progress of the experiments 

 much valuable advice was kindly given by Prof. Christison, 

 some of whose experienced suggestions Avere not fully car- 

 ried out, on account of the sudden interruption of the work. 



The transparency of the young fish renders the central 

 organs of the circulation, as well as the minutest capillary, 

 equally visible, thus affording a much better subject for the 

 examination of irritants and other poisons than the web of a 

 frog's foot, since only a limited area of the vascular system 

 in the latter case can be observed by the exj^erimenter, and 

 better than can be afforded even by the very young tadpole. 



The most numerous experiments Avere those performed 

 with Fleming's Tincture of Aconite. The doses of the drug 



* Extracts from this paper were read at the meeting of the British Asso- 

 ciation last year at Dundee (Sept., 1867). 



