of the Blood and Animal Tissuei. 131 



most delicate test objects, it was impossible to decide the 

 question of superiority between J. J. Lister's microscope, and 

 that which the profound and skilful optician of Modena, had 

 with him during his late visit to this country; although the 

 professor most obligingly afforded every facility for the trial. 



Most of the observations of which I am about to speak, were 

 made in the course of the last spring, when my friend not 

 merely favoured me with the use of his instrument, in order to 

 ascertain the accuracy of some recent microscopic examina- 

 tions, but took upon himself a very active part in the inquiry. 



As we hope, before long, to give a detailed account of our 

 investigations, I shall on the present occasion confine myself 

 to an outline of the facts. 



Particles of the Blood. — In our examination of these cor- 

 puscles, we have in vain looked for the globular form attri- 

 buted to them, not only by the older authors Leeuwenhoeck, 

 Fontana, and Haller, "but still more recently by Sir Everard 

 Home and Bauer. Our observations are also at variance with 

 the opinion long since formed by Hewson, that these particles 

 consisted of a central globule inclosed in a vesicle composed 

 of the coloured part, and which, though refuted by Dr. Young, 

 has since, in a modified form, been revived by Sir Everard 

 Home and Bauer in this country, and by Prevost and 

 Dumas on the Continent. We have never been able to per- 

 ceive the separation of the colouring matter, which our coun- 

 trymen have described as taking place in a few seconds after 

 the particles have escaped from the body ; nor can we with 

 Prevost and Dumas, consider the particles as prominent in 

 the centre. 



The particles of the blood must unquestionably be classed 

 amongst the objects most difficult to examine with the micro- 

 scope ; partly from the variations of form to which their yield- 

 inw structure renders them liable, but still more from their 

 being transparent and composed of a substance which, as Dr. 

 Young lias remarked, is probably not uniform in its refractive 

 power. 



These causes of error we have endeavoured to counteract 

 by varying the mode of observation. We have viewed the 

 particles both wet and dry, both as opaque and as transpa- 

 rent objects, under every variety of power and light, and we 

 lay no stress on observations which have not been confirmed 

 by frequent repetition. 



To us tile particles of human blood appear to consist of 



circular flattened transparent cakes, which, when seen singly, 



appear to be nearly or quite colourless. Their edges are 



S 2 roundrd. 



