370 
rapidity possible, after being shed from the finger, and do 
not doubt that they exist in their peculiar form whilst within 
the body. 
5. Means of studying the changes of the blood-corpuscles in 
disease.—The study of pathological changes in the form- 
elements of the blood, as to their numbers, absolute and rela- 
tive, size, shape, and properties, has hardly been yet attempted. 
Yet it can hardly be doubted that the physician should re- 
ceive as important information from the careful examination 
of the blood in many cases of disease, as he does at present 
from the study of the urine. The reason why the blood is 
almost or totally neglected is, firstly, that the microscopes in 
the hands of most hospital students and practitioners are 
quite inadequate (a power of 200 diameters being their 
highest, whereas 450 is required) ; and, secondly, that 
hitherto the examination of the bluod has been really a very 
difficult matter, requiring great haste and the exercise of 
some skill in drawing. A drop of blood taken from a patient 
must be immediately examined, drawings made, and notes 
written, and then it rapidly begins to change, dries up, and 
is lost. ‘The observer too is never sure that what he may 
have seen is not due to the progressive changes accompany- 
ing the death of the drop of blood before him, and as he can 
never re-examine anything remarkable which he may have 
observed, can have but little confidence in his impressions 
concerning it. Drying has been used as a means of preserv- 
ing blood, but is of very little or no use, since it necessarily 
causes distortion and changes in the corpuscles. All the re- 
agents commonly used in microscopy affect, more or less, the 
form of the corpuscles. If the medical man possessed a re- 
agent which would enable him instantaneously, on removing 
a drop of blood from his patient, to preserve all its form- 
elements absolutely unchanged, and in such a condition that 
he could place the specimen aside, and compare it with other 
cases and with specimens from the same individual from day 
to day, it is likely that our knowledge of pathological changes 
in the blood would advance, and that the condition of the 
blood would be made the subject of study in the wards of 
hospitals. Such a reagent exists in the so-called hyper- 
osmic or osmic acid! introduced as a preservative agent by 
Professor Max Schultze. It is sufficient to expose a thin 
film of blood on a glass cover to the vapour arising from a 
bottle containing the two per cent. solution of osmic acid, 
during three minutes, to ensure its complete preservation.” 
' To be bought of Messrs. Hopkin and Williams. 
? This method is due to Professor Schweigger Seidel, of Leipzig. 
