30° THE MICROSCOPICAL NEWS. 
more difficult to get a fair average by measurements. Moreover, 
the shrinkage of corpuscles in drying may be greater or less under 
different circumstances, and its amount is not yet known with any 
certainty. In any case it must be very slight, to be sure, but in a 
matter of such vital importance it cannot be neglected bythe scientific 
observer, until its amount is known for all circumstances. Grant- 
ing the strong probability that the microscope does, under favourable 
circumstances, afford a means of positively identifying human blood, 
and distinguishing it from all other blood, we must still hold to the 
opinion that, until experience has shown such evidence to be 
sure and infallible, no scientific man is warranted in stating that a 
stain upon cloth is made by human blogd, from the microscopical 
examination alone. f 
Doubtless in the particular case referred to the microscopist was 
fully justified in giving the positive testimony that has been reported, . 
but we would particularly impress upon the reader the uncertainty 
of the microscopical evidence taken alone—it may be justly main- 
tained that such evidence is, to say the least, not infallible. The 
subject having been brought before the public once more it seems 
desirable that microscopists should be reminded that the micro- 
scope cannot be regarded as infallible to distinguish human blood. 
It may be we are conservative about it. We are willing to believe 
that the microscope is capable of identifying human blood from the 
examination of a few dried corpuscles, but the proof that it is so 
seems to us not conclusive. If we err it is upon the side of safety; 
and to those readers who have had no practical acquaintance with 
such examinations we would say, do not be led into error by the 
apparent simplicity of the problem. If human blood can be 
identified with the microscope it can only be done with safety by 
persons of great experience in the examination and measurement 
of blood-cells.— Zhe American Monthly Microscopical Journal. 
SELAGINELLA: ALTERATION OF 
GENERATIONS. 
By W. STANLEY. * 
N drawing your attention this evening to this family of Crypto- 
gamous plants I do so for two reasons. In the first place, 
although it has most important botanical characteristics, it may be 
said to be very little known amongst botanists in general ; and in 
* A paper read before the Manchester Microscopical Society, Jan. 3, 1884. 
