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Royal Microscopical Society. 
and are, like the crystals, slowly extracted by water. The amor- 
phous form is well represented in the coloured figure No. 2, 
Taf. viii., in Ultzmann and Hofmann’s Atlas. 
A spherical form of what is generally supposed to be urate of 
soda has been represented by Dr. Golding Bird, Dr. Thudichum, 
Dr. Roberts, Dr. Beale, and Drs. Ultzmann and Hofmann. It con- 
sists of small, very perfectly-outlined spheres, which, as Dr. Beale 
describes them, are of great lustre, and which have usually spikelets 
of uric acid deposited on their surface. They are said to be found 
chiefly in the urine of children, and of persons in a feverish state 
(Dr. Beale) ; in the long-retained urine of children in fever (Dr. 
Roberts) ; in the urine of persons labouring under fever who were 
treated' with carbonate of soda (Dr. Golding Bird); in the urine 
of children suffering from petechial typhus not treated by carbonate 
of soda, from measles, and from scarlatina (Dr. Thudichum). Drs. 
Ultzmann and Hofmann give, besides these, figures of large, some- 
what irregular crystalline dumb-bells from the urine of a child 
suffering from intestinal catarrh. 
Dr. Thudichum* states that if a solution of urate of soda he 
allowed to evaporate spontaneously, the salt is deposited in simple 
spherical masses and granules. Dr. Beale t gives twice a drawing 
of large spheres of urate of soda with halo of fine radiating needles, 
obtained by concentrating healthy urine; and also a drawing of 
some very large spheres from a case of remittent fever (sent by 
Dr. Kennion). 
It may be assumed that the needles are to he regarded as 
crystals, though their appearance of flexibility, their remarkable 
tenuity, and the absence from them of indications of angularity 
of section are departures from the typical qualities of the crystal. 
They are to my mind crystals with definite colloidal affinities. 
Assuming that the needles are crystals, they occur where, pritna 
facie, crystals ought not to he looked for. Crystallizable matters 
of low solubility deposited in a colloid such as the substance of carti- 
lage, deposited moreover at the comparatively high temperature of 
the body, might, according to our experience, be expected to affect 
a spheroidal form. The departure from the rule is so startling 
as to make it probable that when the conditions are fully known 
much addition to our knowledge of the working of the rule may be 
hoped for. 
Conversely, the same substance which forms crystals in the pre- 
sence of colloids, forms spheres where the influence of colloids is less 
manifest or is absent. Here again extended observation of condi- 
tions is necessary. 
I will now relate a series of experiments affecting the habits 
* ‘ Pathology of the Urine,’ p. 91. 
f ‘ Kidney Diseases, Urinary Deposits,’ &c., 1868. 
