581 
COAL-TAR SOAP. 
K no wing the eliicac}^ of tar in many skin affections, we 
have thought the following formula, recommended by 
M. Demeaux, and extracted from the Pharmaceutical Journal, 
might be resorted to, especially for the dog. 
Equal parts of coal-tar, soap, and alcohol, are to be heated 
together in a bath until complete solution is effected, and on 
cooling, a very soluble soap is produced, which, with water, 
makes a stable emulsion. 
It may be used in any degree of concentration, being very 
manageable, and its great solubility in cold or warm water, 
prevents it permanently soiling any substance it comes in 
contact with. 
BLOOD-CORPUSCLES IN THE RETINA. 
Dr. L. Reuben, of New York, on looking through a thick 
plate of blue cobalt glass at a clear, bright sky, observed an 
appearance of movement of numerous minute, shining, lucid 
points, or bead-like bodies. These movements or impulsions 
were synchronous with the pulsations of the heart, and in all 
directions. These and other facts he states to be in agree¬ 
ment with the hypothesis that the lucid lines are quasi-visible 
traces of the corpuscles of the blood moving in the vessels of 
the retina. 
THE THREE PRIMARY COLOURS. 
Professor J. C. Maxwell, in a lecture lately delivered 
at the Royal Institution, asserted that the three primary 
colours are red, green, and blue; not red, yellow, and blue, as 
accepted by Dr. Brevvster and others. These colours were 
exhibited by him on a screen by means of three lanterns, 
before which were placed glass troughs containing respectively 
sulpho-cyanide of iron, chloride of copper, and ammoniated 
copper. On mixing these colours he found yellow to be 
produced by the red and green, purple by red and blue, a 
pale pink by blue and yellow, and the three together pro¬ 
duced white. 
