476 PROF. G. GULLIVER ON [June 15, 
The present Tables, though so extensive, show how numerous are 
the Vertebrates of which we still require an examination of the blood- 
corpuscles. The sum of the facts at this time known on the subject 
is so far imperfect, that we are ignorant of how svon new ones may 
turn up to subvert even our most cherished theories or generaliza- 
tions. Hence the remarks or deductions on the present occasion, 
being confined to the measurements given in the Tables, must be 
considered as provisional, subject to modifications or corrections to 
suit the advance of knowledge, especially as regards Fishes, Batra- 
chians, Cetaceans, Sirenians, and some other Vertebrates. It is 
desirable, too, that my measurements should be subjected to expe- 
rimental examinations by independent observers. 
To rigorous accuracy these Tables, of the averages of a far greater 
number of measurements, have no pretension. In this respect all 
that can be candidly said is, that, though they have been carefully 
deduced from innumerable and generally correct observations of the 
corpuscles, the size of these is by no means invariable in a single 
species, and that, even were they ever so constant in magnitude, 
seeing how much they usually differ among themselves in every field 
of vision, commonly to the extent of one third larger or smaller than 
the mean, their average dimensions could not be easily determined 
with sure precision. Upwards of a third of a century has passed 
since Dr. Bowerbank, experimenting with a cobweb micrometer at 
one of his delightful and instructive entertainments, found a remark- 
able difference in the size of the red blood-corpuscles obtained from 
the fingers of three gentlemen among his guests then present toge- 
ther. In the human subject I have often observed similar diver- 
sities, though to a less extent than appeared in Dr. Bowerbank’s 
experiments ; and I have notes of results to the like effect of obser- 
vations, long since made by me, on single and on different individuals 
of one and the same species of all the Vertebrate classes. But such 
variations (in Man, see further p. 484), whether in a single individual 
or in different individuals of one species, are confined within such 
limits as not to prevent good approximations to the truth in the 
measurements. 
It should also be borne in mind that small organisms, even when 
each of them has a fixed diameter, vary so much among themselves 
that it would be difficult, if not impossible, to determine with abso- 
Inte precision their mean dimensions, however easy it may be to 
measure truly a single blood-disk or a spore of a cryptogam. For 
example, let any person make trials with several portions of one and 
the same sample of spores or little seeds of a plant, when the results 
of numerous true measurements will fail to afford precisely the same 
average diameter. How, then, can this be expected of objects so 
variable in size and shape as the red blood-corpuscles? Those of 
Mammalia, when dried slowly, are apt to become misshapen and 
more or less irregularly contracted ; but when dried instantaneously 
in single or very thin layers on a glass slide, their form is admirably 
preserved, and their size is a shade larger than in the wet state, 
especially when prepared in summer. The pyrenzematous corpuscles, 
